Author: Tammy Plotner

Object Name: Messier 106
Alternative Designations: M106, NGC 4258
Object Type: Sbp Spiral Galaxy
Constellation: Canes Venetici
Right Ascension: 12 : 19.0 (h:m)
Declination: +47 : 18 (deg:m)
Distance: 25000 (kly)
Visual Brightness: 8.4 (mag)
Apparent Dimension: 19×8 (arc min)

Locating Messier 106: To begin in roughly the correct area to locate M106, identify the bottom corner star (towards the handle) of the Big Dipper asterism. This is Gamma Ursa Majoris. Now, locate Alpha Canes Venetici – Cor Caroli – about a fistwidth southeast. You will know if you have the correct star because Cor Caroli is an easily split double that will reveal itself to both binoculars, finderscopes and small telescopes. Now start your hunt for M106 directly between Gamma UM and Alpha CVn. At nearly magnitude 8, M106 can be spotted in most binoculars from a dark sky site and is easily seen in all telescopes. Unlike most galaxies, it is bright enough to stand up to moderate light pollution and resolves its structure well in larger instruments.

What You Are Looking At: Located roughly 25 million light years away, M106 may be a member of a small galaxy cloud that centers around Ursa Major. It has a great spiral structure, but many hidden facets. “It has been claimed that the megamaser observations of the nucleus of NGC 4258 show that a massive black hole is present in its center. We show that the evidence of ejection of gas, radio plasma, and X-ray emitting QSOs from this nucleus all show that the ejection is coming from the center in a curving flow within a cone with angle ~40 degrees, centered at P.A. 100 degrees.” says E.M. Burbidge abd G. Burbidge of the University of California, San Deigo. “This is close to the direction in which the velocities from the megamaser have been measured, so that the evidence taken as a whole suggests that the masering gas also is being ejected in the same direction at velocities +/- 900 km/sec and not rotating about a massive black hole. Thus it does not provide evidence for a black hole in the center.”

However, not every study agrees with that. “The sub-parsec masing disk recently found to be orbiting a central mass in the Seyfert/LINER galaxy NGC~4258 provides the most compelling evidence to date for the existence of a massive black hole in the nucleus of a galaxy. The disk is oriented nearly edge-on and the X-ray spectrum is heavily absorbed. Therefore, in this galaxy, the optical emission-line spectrum generally exhibited by an active galactic nucleus is perhaps best sought using polarized light: probing for light scattered off material surrounding the central source.” says Belinda J. Wilkes (et al). “New polarimetry of NGC~4258 has uncovered a compact polarized nucleus whose spectrum consists of a faint blue continuum similar to those of unobscured quasars, plus broadened emission lines. The lines are strongly linearly polarized ($5-10$%) at a position angle coincident with the plane of the maser disk. This result provides substantiating evidence for a weakly active central engine in NGC~4258 and for the existence of obscuring, orbiting tori which impart many of the perceived distinctions between various types of active galaxy.”

And indeed the central core region – and its accompanying accretion disc continue to fascinate astronmers. “A wealth of new information about the structure of the maser disk in NGC 4258 has been obtained from a series of 18 VLBA observations spanning three years, as well as from 32 additional epochs of spectral monitoring data from 1994 to the present, acquired with the VLA, Effelsberg, and GBT. The warp of the disk has been defined precisely. The thickness of the maser disk has been measured to be 12 micro-arcseconds (FWHM), which is slightly smaller than previously quoted upper limits. Under the assumption that the masers trace the true vertical distribution of material in the disk, from the condition of hydrostatic equilibrium the sound speed is 1.5 km s?1, corresponding to a thermal temperature of 600K.” says James M. Moran (et al).

“The accelerations of the high velocity maser components have been accurately measured for many features on both the blue and red side of the spectrum. The azimuthal offsets of these masers from the midline (the line through the disk in the plane of the sky) and derived projected offsets from the midline based on the warp model correspond well with the measured offsets. This result suggests that the masers are well described as discrete clumps of masing gas, which accurately trace the Keplerian motion of the disk. However, we have continued to search for evidence of apparent motions caused by “phase effects.” This work provides the foundation for refining the estimate of the distance to NGC 4258 through measurements of feature acceleration and proper motion. The refined estimate of this distance is expected to be announced in the near future.”

But that’s not all that’s hidden. Try magnetic interaction of jets and molecular clouds in NGC 4258! “NGC 4258 is a well known spiral galaxy with a peculiar large scale jet flow detected in the radio and in H alpha. Due to the special geometry of the galaxy, the jets emerge from the nuclear region through the galactic disk – at least in the inner region. Also the distribution of molecular gas looks different from that in other spiral galaxies: 12CO(1-0) emission has only been detected in the center and along the jets and only up to distances of about 50” (1.8 kpc) from the nucleus. This concentration of CO along the jets is similar to what is expected as fuel for jet-induced star formation in more distant objects. The reason for the CO concentration along the inner jets in NGC 4258 was not understood and is the motivation for the observations presented here.” says M. Krause (et al).

“We detected two parallel CO ridges along a position angle of -25° with a total length of about 80” (2.8 kpc), separated by a CO depleted funnel with a width of about 5” (175 pc). The Halpha emission is more extended and broader than the CO emission with its maximum just in between the two CO ridges. It seems to be mixed in location and in velocity with the CO emission. In CO we see a peculiar velocity distribution in the iso-velocity map and p-v diagrams. We discuss different scenarios for an interpretation and present a model which can explain the observational results consistently. We propose here that the concentration of CO along the ridges is due to interaction of the rotating gas clouds with the jet’s magnetic field by ambipolar diffusion (ion-neutral drift). This magnetic interaction is thought to increase the time the molecular clouds reside near the jet thus leading to the quasi-static CO ridge.”

History: M106 was discovered by Pierre Mechain in July 1781. In his personal letters to Bernouli he writes: “In July 1781 I found another nebula close to the Great Bear [Ursa Major] near the star No. 3 of the Hunting Dogs [Canes Venatici] and 1 deg more south, I estimate its right ascension 181d 40′ and its northern declination about 49d. I will be going to determine the more accurate position of this one shortly.” It was later independently rediscovered by William Herschel on March 9, 1788 who pens in his notes: “Very brilliant. Bright Nucleus. With faint milky branches north preceding and south following. 15′ long and to the south following running into very faint nebulosity extending a great way. The nucleus is not round.”

Roughly a half century later it would be observed and cataloged by Admiral Smyth who said: “A large white nebula, closely following the haunches of the Greater Bear, discovered by WH [William Herschel] in 1788, and No. 1175 of his son’s Catalogue. It is a noble-sized oval, trending rather from the vertical in a direction np [north preceding, NW] and sf [south following, SE], with a brightish nucleus in its southern portion; the lateral edges are better defined than the ends. It is preceded by two stars of the 10th magnitude, and followed by two others; and there are also some minute points of light in the field, seen occasionally by glimpses. This object was carefully differentiated with Alkaid; and its place will be indicated by a running diagonal line across the square of Ursa Major, from Alpha through Gamma, and carrying it 7 1/2 deg into the south-east, that is, a little less than the distance between those stars.”

Enjoy your observations!

Top M106 image credit, Palomar Observatory courtesy of Caltech, M106 Hubble Image, M106 SSDS Image, M106 courtesy of Western Washington University, M106 Core courtesy of Lowell Observatory, M106 2MASS Image, M106 image courtesy of Hunter Wilson (Wikipedia) and M106 image courtesy of N.A.Sharp, REU program NOAO/AURA/NSF.

Object Name: Messier 105
Alternative Designations: M105, NGC 3379
Object Type: E1 Elliptical Galaxy
Constellation: Leo
Right Ascension: 10 : 47.8 (h:m)
Declination: +12 : 35 (deg:m)
Distance: 38000 (kly)
Visual Brightness: 9.3 (mag)
Apparent Dimension: 2.0 (arc min)

Locating Messier 105: Begin your starhop for this great galaxy by identifying Alpha Leonis (Regulus), the brightest star in the backwards question mark that is the signature asterism of the constellation of Leo. Now, look east for the shallow triangle that marks the Lion’s hips. Your next marker is the southwestern star – Theta. Between them, on the belly of the Lion, you will see another faint, but unaided eye visible star. You’ll find Messier 105 just about two degrees (a fingerwidth) to the southeast of this star. If you cannot see this star, chances are you won’t be able to see this egg-shaped elliptical galaxy, either. From a clear, dark sky it can be spotted in larger binoculars and is fairly easy with a small telescope. While larger aperture will make the galaxy appear brighter and somewhat misty around the edges, elliptical galaxies do not produce much detail.

What You Are Looking At: Hanging out with the Leo 1 galaxy group some 38 million light years from our solar system, this ancient galaxy sports a core region that contains about 50 million times more mass than our own Sun. What is it? You got it. A black hole. “We combine Hubble Space Telescope spectroscopy and ground-based integral-field data from the SAURON and OASIS instruments to study the central black hole in the nearby elliptical galaxy NGC 3379. These models also probe the velocity distribution in the immediate vicinity of the black hole and reveal a nearly isotropic velocity distribution throughout the galaxy and down to the black hole sphere of influence RBH. The morphology of the nuclear gas disc suggests that it is not in the equatorial plane; however the core of NGC 3379 is nearly spherical. Inclined thin-disc models of the gas find a nominal black hole of mass (2.0 +/- 0.1) × 108Msolar (3sigma errors), but the model is a poor fit to the kinematics. The data are better fit by introducing a twist in the gas kinematics (with the black hole mass assumed to be 2.0 × 108Msolar), although the constraints on the nature and shape of this perturbation are insufficient for more detailed modelling.” says K.A. Shapiro (et al). “Given the apparent regularity of the gas disc appearance, the presence of such strong non-circular motion indicates that caution must be used when measuring black hole masses with gas dynamical methods alone.”

And it is the gas (or lack thereof) that keeps astronomers going back to study M105. Is it possible that there is not only one – but two – black holes within its core? “Such a small amount of gas can be supplied by stellar mass loss in only 107 yr. Thus, the gas must be accreting into the central supermassive black hole at a very low radiative efficiency as in the ADAF or RIAF models, or it is being expelled in a galactic wind driven by the same AGN feedback mechanism as that observed in cluster cooling flows. If the gas is being expelled in an AGN-driven wind, then the ratio of mechanical to radio power of the AGN must be 104, which is comparable to that measured in cluster cooling flows that have recently been perturbed by radio outbursts. Only 8% of the detected point sources are coincident with globular cluster positions, which is significantly less than that found among other elliptical galaxies observed by Chandra. The low specific frequency of globular clusters and the small fraction of X-ray point sources associated with globular clusters in NGC 3379 is more similar to the properties of lenticular galaxies rather than elliptical galaxies.” says Laurence P. David, (et al).

“The brightest point source in NGC 3379 is located 360 pc from the central AGN with a peak luminosity of 3.5 × 1039 ergs s-1, which places it in the class of ultraluminous X-ray point sources (ULXs). Analysis of an archival ROSAT HRI observation of NGC 3379 shows that this source was at a comparable luminosity 5 yr prior to the Chandra observation. The spectrum of the ULX is well described by a power-law model with ? = 1.6 ± 0.1 and galactic absorption, similar to other ULXs observed by Chandra and XMM-Newton and to the low-hard state observed in Galactic black hole binaries. During the Chandra observation, the source intensity smoothly varies by a factor of 2 with the suggestion of an 8-10 hr period. No changes in hardness ratio are detected as the intensity of the source varies. While periodic behavior has recently been detected in several ULXs, all of these reside within spiral galaxies. The ULX in NGC 3379 is the only known ULX in an elliptical galaxy with a smoothly varying light curve suggestive of an eclipsing binary system.”

Is this structure a probable result of interaction with neighboring galaxies in the group? “The central regions of the three brightest members of the Leo I galaxy group—NGC 3368, NGC 3379, and NGC 3384—are investigated by means of two-dimensional spectroscopy. In all three galaxies we have found separate circumnuclear stellar and gaseous subsystems—more probably, disks—whose spatial orientations and spins are connected to the spatial orientation of the supergiant intergalactic H i ring reported previously by Schneider et al. and Schneider. In NGC 3368 the global gaseous disk seems also to be inclined to the symmetry plane of the stellar body, being probably of external origin.” says O. K. Sil’chenko (et al). “Although the rather young mean stellar age and spatial orientations of the circumnuclear disks in NGC 3379, NGC 3384, and NGC 3368 could imply their recent formation from material of the intergalactic H i cloud, the timescale of these secondary formation events, on the order of 3 Gyr, does not support the collision scenario of Rood & Williams but is rather in line with the ideas of Schneider regarding tidal interactions of the galaxies with the H i cloud on timescales of the intergroup orbital motions.”

History: M105 was discovered by Pierre Mechain on March 24, 1781, actually 3 days before catalog number M101 was discovered. Although most claim there wasn’t any reason that it wasn’t included in Charles Messier’s published list, it was a bad time for Messier who had just lost his wife and newborn son and it would be easy to make a mistake or overlook an observation. Mechain described this object in his letter of May 6, 1783: “Mr. Messier mentions there on page 264 and 265 two nebulous stars, which I have discovered in the Lion [Leo; M95 and M96]. I find nothing to correct for the given positions which I have determined by comparison of their situation with respect to Regulus. There is, however, a third one, somewhat more northerly, which is even more vivid [brighter] than the two preceding ones [M95 and M96]. I discovered this one on March 24, 1781, 4 or 5 days after I had found the other two. On April 10, I compared its situation with Gamma Leonis from which followed its right ascension 159d 3′ 45″ and its northern declination of 13d 43′ 58”.

Messier 105 would be later recovered by Sir William Herschel who believed he was looking at multiple nebulae: “If it was supposed that double nebulae at some distance from each other would frequently be seen, it will now on the contrary be admitted that an expectation of finding a great number of attracting centers in a nebulosity of no great extent is not so probable; and accordingly observation has shewn that greater combinations of nebular than those of the foregoing article.” His son, John, would also observe M105 and give it a catalog designation as well.

However, it was Admiral Smyth who described it eloquently; “A pair of bright-class nebulae, sp [south preceding, SW] and nf [north following, NE] of each other, on the Lion’s belly, discovered by WH [William Herschel] in March, 1783, and No. 758 [NGC 3384] in his son’s Catalogue; while at a small distance to the nf [north following, NE] is a neat but minute double star. These are two of the three nebulae described by both Herschels [M105 and NGC 3384]; but the third [NGC 3389] I cannot distinguish, unless it be a glow in the sf [south following, SE], in a vertical line with two small stars. We now approach a region where these mysterious luminous masses are scattered over the vast concavity of the heavens, in truly boundless profusion; and in them, all true Herschelians must view mighty laboratories of the Universe, in which are contained the principles of future systems of suns, planets and satellites! The objects here treated of, are among the nebulae included within a round patch of about 2 deg or 3 deg in diameter, in the apparently starless space of the Lion’s loins. Now the observer unprovided with an equatorial instrument – and unfortunately many of Urania’s most zealous followers are in that predicament – may wish to fish it up. If his telescope be of capacity for grasping sufficient light, the field may be found, under a moderate power, south of the line which joins Regulus and Theta Leonis about 10 deg east of, and nearly on the parallel with, the former.”

Enjoy your own look into these “mighty laboratories of the universe”!

Top M105 image credit, Palomar Observatory courtesy of Caltech, M105 Black Hole courtesy of Karl Gebhardt (University of Michigan), Tod Lauer (NOAO), and NASA, M105 rotation courtesy of Ohio State University, M105 2MASS image, M105 group image by Isaac Newton Telescope and M105 image courtesy of NOAO/AURA/NSF.

Object Name: Messier 104
Alternative Designations: M104, NGC 4594, The Sombrero Galaxy
Object Type: Type Sa Spiral Galaxy
Constellation: Virgo
Right Ascension: 12 : 40.0 (h:m)
Declination: -11 : 37 (deg:m)
Distance: 50000 (kly)
Visual Brightness: 8.0 (mag)
Apparent Dimension: 9×4 (arc min)

Locating Messier 104: M104 is easily found exactly 11 degrees – about a fistwidth – due west of Alpha Virginis (Spica). With excellent conditions from a dark sky site, it can be spotted in binoculars as a small, eye-shaped patch of nebulosity. With telescopes as small as 3″ in aperture, it takes on a galactic signature and reveals its dark dustlane beginning at about 4.5″ in aperture. The more light gathering ability, the more the beautiful Sombrero Galaxy reveals! As always, galaxies prefer dark sky sites and good seeing conditions.

What You Are Looking At: The Sombrero, also known as M104, is one of the largest galaxies in the nearby Virgo cluster, about 28 million light years from Earth. This Great Observatories view of the famous Sombrero galaxy was made using NASA’s Chandra X-ray Observatory, Hubble Space Telescope and Spitzer Space Telescope. The main figure shows the combined image from the three telescopes, while the three inset images show the separate observatory views. The Chandra X-ray image (in blue) shows hot gas in the galaxy and point sources that are a mixture of objects within the Sombrero as well as quasars in the background. The Chandra observations show that diffuse X-ray emission extends over 60,000 light years from the center of the Sombrero. (The galaxy itself spans 50,000 light years across.) Scientists think this extended X-ray glow may be the result of a wind from the galaxy, primarily being driven by supernovas that have exploded within its bulge and disk. The Hubble optical image (green) shows a bulge of starlight partially blocked by a rim of dust, as this spiral galaxy is being observed edge on. That same rim of dust appears bright in Spitzer’s infrared image, which also reveals that Sombrero’s central bulge of stars.

Like “Diamonds on the Hat”, globular clusters are all parcel and part of M104’s makeup. “Images from the Hubble Space Telescope Advanced Camera for surveys are used to carry out a new photometric study of the globular clusters (GCs) in M104, the Sombrero galaxy. The primary focus of our study is the characteristic distribution function of linear sizes [size distribution function (SDF)] of the GCs. We measure the effective radii for 652 clusters with point spread function-convolved King and Wilson dynamical model fits. The SDF is remarkably similar to those measured for other large galaxies of all types, adding strong support to the view that it is a ‘universal’ feature of GC systems. We use the Sombrero and Milky Way data and the formation models of Baumgardt & Kroupa (2007) to develop a more general interpretation of the SDF for GCs. We propose that the shape of the SDF that we see today for GCs is strongly influenced by the early rapid mass loss during their star-forming stage, coupled with stochastic differences from cluster to cluster in the star formation efficiency (SFE) and their initial sizes. We find that the observed SDF shape can be accurately predicted by a simple model in which the protocluster clouds had characteristic sizes of 0.9 ± 0.1 pc and SFEs of 0.3 ± 0.07 .” says Wlliam E. Harris (et al).

“The colours and luminosities of the M104 clusters show the clearly defined classic bimodal form. The blue sequence exhibits a mass/metallicity relation, following a scaling of heavy-element abundance with luminosity of Z?L0.3 very similar to what has been found in most giant elliptical galaxies. A quantitative self-enrichment model provides a good first-order match to the data for the same initial SFE and protocluster size that were required to explain the SDF. We also discuss various forms of the GC Fundamental Plane of structural parameters and show that useful tests of it can be extended to galaxies beyond the Local Group. The M104 clusters strongly resemble those of the Milky Way and other nearby systems in terms of such test quantities as integrated surface density and binding energy.”

But, just like our own galaxy, globular clusters aren’t all that’s hiding inside that awesome halo. “We used the CTIO 4m telescope to make a complete and kinematically unbiased survey of M104 (NGC 4594; the Sombrero galaxy) for planetary nebulae (i.e., stars) out to 16 kpc. We present the positions and monochromatic [O III] lambda 5007 magnitudes of 294 planetaries, and use the observed planetary nebula luminosity function (PNLF) to measure a distance of 8.9+/-0.6Mpc to the galaxy. The luminosity-specific PN number lambda 2.5 in the halo of M104 is approximately 21.7×10^-9^L_{sun}_, which for its color (B-V)=0.95, is comparable to the values in other galaxies.” says H.C. Ford (et al).

“We use the PNLF distance to M104 to compare its luminosity to the luminosities of the brightest galaxies in the Virgo Cluster, finding that if M104 were in the Virgo Cluster, it would be the third brightest galaxy. We combined the PNLF distance and the observed velocity corrected for Virgo infall to calculate a Hubble constant H_0_=91+/-8km/s/Mpc. We also used the PNLF distances to the NGC 1023 group, the Leo group, the Virgo Cluster, and the Fornax Cluster to derive Hubble constants corrected for Virgo infall. The values of H_0_ for M104, the NGC 1023 group, the Virgo Cluster, and the Fornax Cluster are in excellent agreement, suggesting that the PNLF distances and Schechter’s linear infall model provide a self-consistent representation of the Hubble expansion and Virgo infall within most regions of the local supercluster.”

History: Messier 104 was not included in Messier’s originally published catalog. However, Charles Messier added it by hand to his personal copy on May 11, 1781, and described it as a “very faint nebula.” It was Camille Flammarion who found that its position coincided with Herschel’s H I.43, which is the Sombrero Galaxy (NGC 4594), and added it to the official Messier list in 1921. This object is also mentioned by Pierre Mechain as his discovery: “On May 11, 1781, I discovered a nebula above the Raven [Corvus] which did not appear to me to contain any single star. It is of a faint light and difficult to find if the micrometer wires are illuminated. I have compared it [its position] on this day and the following with Spica in the Virgin and from this derived its right ascension 187d 9′ 42″ and its southern declination 10d 24′ 49″ [the same position as in Messier’s handwritten note]. It does not appear in the Connoissance des Temps.”

William Herschel found this object independently on May 9, 1784, but it would be his son John who would first notice there was something a bit different about it: “There is a faint diffused oval light all about it, and I am almost positive that there is a dark interval or stratum separating the nucleus and general mass of the nebula from the light above (s of) it. Surely no illusion. There is a faint diffused oval light all about it, and I am almost positive that there is a dark interval or stratum separating the nucleus and general mass of the nebula from the light above (south of) it.”

Enjoy your observations of this great galaxy!

Top M104 image credit, Palomar Observatory courtesy of Caltech, M104 Composite – Spitzer, Chandra and Hubble, M104 Hubble Remix, M104 Hubble Details, M104 Spitzer Image and M104 image courtesy of Todd Boroson/NOAO/AURA/NSF.

Object Name: Messier 103
Alternative Designations: M103, NGC 581
Object Type: Type D Open Cluster
Constellation: Cassiopeia
Right Ascension: 01 : 33.2 (h:m)
Declination: +60 : 42 (deg:m)
Distance: 8.5 (kly)
Visual Brightness: 7.4 (mag)
Apparent Dimension: 6.0 (arc min)

Locating Messier 103: Locating M103 is fairly easy even under moderately light polluted conditions. Simply identify Delta Cassiopeiae (Ruchbah), a bright, blue-white star that marks one of the lower positions of Cassiopeia’s class “W” asterism. Simply center it in the finderscope and look about 1/2 a degree north and 1 degree east in the direction of Epsilon. In binoculars and a finderscope it will appear as a diamond shape patch of nebulosity which tries to resolve and will reveal its individual stars to even a small telescope. Loosely constructed, M103 makes a wonderful target for urban skies and less than perfect sky conditions.

What You Are Looking At: Located some 8,500 light years away and spanning over an area about 15 light years wide, this 25 million year old star cluster can sometimes be a little hard to pick out of the surrounding star field because of its wide open profile. Notable non-member binary Struve 131 dominates the scene, and only through radial velocity studies has genuine cluster members been identified. “The cluster has been assigned a class III2p by Ruprecht {1966). Oja (1966) determined the membership of the stars for the cluster on the basis of a proper motion study and reported 73 stars to be its possible members. Out of these, UBV photoelectric magnitudes and colors are presently known for only twenty stars.” says Ram Saga arid U.C. Joshi.

But look for M103’s prominent red giant! Is there a special reason? Yes. “A statistical research on evolved stars beyond hydrogen exhaustion is performed by comparing the H-R diagrams of about 60 open clusters with a set of isochronous curves without mass loss derived from Iben’s evolutionary tracks and time scales for Population I stars.” says G. Barbaro (et al). “Although evidence concerning mass loss from stars of different types and especially red giants and supergiants is gradually increasing, still not much is known about the real causes and the quantitative aspects of this phenomena, so that up to know little can be foretold concerning its bearing on stellar evolution.”

History: This sparkling open cluster was discovered by Pierre Mechain in either March or April of 1781and added by Charles Messier to his catalog before he had a chance to observe it. From Mechain’s notes: “Cluster of stars between Epsilon and Delta of the leg of Cassiopeia.”

Sir William Herschel would capture it again on August 8, 1783 when he describes: “14 or 16 pL. [pretty large (bright)] stars with a great many eS. [extremely small (faint)] ones. Two of the large [bright] ones are double, one of the 1st the other of the 2nd class. (*) The compound eye glass shews a few more that may be taken into the cluster so as to make them about 20. I exclude a good many straggling ones, otherwise there would be no knowing where to stop.”

But observing M103, didn’t stop and it would be Admiral Smyth who would be the first to see red. “”A neat double star in a cluster, on Cassiopeia’s knee, about a degree to nf of Delta. A 7 [th mag], straw coloured; B 9, dusky blue. This is a fan-shaped group, diverging from a sharp star in the nf quadrant. The cluster is brilliant from the splash of a score of its largest members, the four principle ones of which are from the 7th to the 9th magnitude; and under the largest, in the sf, is a red star of the 8th magnitude, which must be that mentioned by JH [John Herschel], No. 126 of his Catalogue of 1833. My attention was first drawn to this object, by seeing it among Srtuve’s acervi (double stars); but soon found that it was also the 103 which Messier describes so vaguely, as being between Delta and Epsilon Cassiopeiae, whereas it is pretty close to Delta, on the Lady’s knee.”

Look for the colors and enjoy your observations!

Top M103 image credit, Palomar Observatory courtesy of Caltech, M103 – Roberto Mura – Wikipedia Image, M103 2MASS image and M103 image courtesy of NOAO/AURA/NSF.

Object Name: Messier 102
Alternative Designations: M102, NGC 5866, The Spindle Galaxy
Object Type: Lenticular Galaxy
Constellation: Draco
Right Ascension: 15 : 06.5 (h:m)
Declination: +55 : 46 (deg:m)
Distance: 45000 (kly)
Visual Brightness: 9.9 (mag)
Apparent Dimension: 5.2×2.3 (arc min)

Locating Messier 102: Locating Messier 102 isn’t particularly easy and will require a good start chart and some work. It’s rough location is about 10 degrees east/northeast of Eta Ursa Major – or about 10 degrees south of Gamma Ursa Minor. It will require at least a 4″ telescope at a relatively dark sky to be seen brightly, and will begin to show both structure and its dark dustlane at apertures approaching 6-8″. For smaller scopes, it will appear as a thin streak of nebulosity. If you are at a very dark sky site, you can use Iota Draconis and shift about 3 deg southwest in the direction of Eta Ursae Majoris or use Theta Bootis where M102 is just to the south.

What You Are Looking At: Located some 45 million light-years and part of a galaxy grouping, M102 is a wonderful lenticular galaxy seen almost edge-on. And seeing is believing! From this beautiful Hubble image and the words of Bill Keel: “The dust lane is slightly warped compared to the disk of starlight. This warp indicates that NGC 5866 may have undergone a gravitational tidal disturbance in the distant past, by a close encounter with another galaxy. This is plausible because it is the largest member of a small cluster known as the NGC 5866 group of galaxies. The starlight disk in NGC 5866 extends well beyond the dust disk. This means that dust and gas still in the galaxy and potentially available to form stars does not stretch nearly as far out in the disk as it did when most of these stars in the disk were formed.”

“The Hubble image shows that NGC 5866 shares another property with the more gas-rich spiral galaxies. Numerous filaments that reach out perpendicular to the disk punctuate the edges of the dust lane. These are short-lived on an astronomical scale, since clouds of dust and gas will lose energy to collisions among themselves and collapse to a thin, flat disk. For spiral galaxies, the incidence of these fingers of dust correlates well with indicators of how many stars have been formed recently, as the input of energy from young massive stars moves gas and dust around to create these structures. The thinness of dust lanes in S0s has been discussed in ground-based galaxy atlases, but it took the resolution of Hubble to show that they can have their own smaller fingers and chimneys of dust.”

But what happens when the stars are done forming? Take a look in infrared… “S0 galaxies are often thought to be passively evolved from spirals after star formation is quenched. To explore what is actually occurring in such galaxies, we present a multi-wavelength case study of NGC 5866—a nearby edge-on S0 galaxy in a relatively isolated environment. This study shows strong evidence for dynamic activities in the interstellar medium, which are most likely driven by supernova explosions in the galactic disk and bulge.” says Jiang-Tao Li (et al).

“Understanding these activities can have strong implications for studying the evolution of such galaxies. We utilize Chandra, Hubble Space Telescope, and Spitzer data as well as ground-based observations to characterize the content, structure, and physical state of the medium and its interplay with the stellar component in NGC 5866. A cold gas disk is detected with an exponential scale height of ~102 pc. Numerous distinct off-disk dusty spurs are also clearly present: prominent ones can extend as far as ~3 × 102 pc from the galactic plane and are probably produced by individual SNe, whereas faint filaments can have ~kpc scale and are likely produced by SNe collectively in the disk/bulge.”

But what’s hot can also be very cool… and it the Spindle Galaxy’s case it the amount of interstellar medium. Says G.K. Kacprzak (New Mexico State University) and G.A. Welch (Saint Mary’s University): “The nearly edge-on S0 galaxy NGC 5866 is notable for its massive molecular interstellar medium, prominent central dust lane, and large IRAS 100 micron flux. The galaxy is relatively isolated, and neither the kinematics nor morphology of the gas suggests that a merger has taken place. Instead, NGC 5866 may be entering an era of star formation fueled with gas donated by its aging stellar population. Are we seeing a counter example of the popular view that galaxies evolve through mergers? We explore that possibility using multi-transition CO observations and SCUBA (Submillimetre Common-User Bolometer Array) imagery of NGC 5866. We analyze the dust and gas components of the interstellar medium using techniques such as the large velocity gradient (LVG) models and a three-dimensional Monte Carlo radiation transfer code. A comparison of SCUBA and appropriately convolved H alpha images reveals both to have similar structure and morphology. This complements the fact that the SCUBA fluxes were under predicted by the Monte Carlo code which does not take star formation into account. Both of those facts indicate that NGC 5866 is indeed under going star formation.”

History: NGC 5866 was probably first turned up by Pierre Mechain during March 1781 – or was observed by Charles Messier himself around that time. Despite Mechain’s disclaimer 2 years later, chances are good that NGC 5866 is object #102 rather than a reclassification of Messier 101. (Considering the personal problems Messier was having during that period, it’s small wonder that an error could have been made.) While Messier orginally added it to his published catalog without verifying its position, he did return later to verify this beautiful galaxy was almost exactly 5 degrees preceding (west) of the actual position previously published. In his 1781 personal notes, Messier writes: “Nebula between the stars Omicron [actually Theta] Bootis and Iota Draconis: it is very faint; near it is a star of the sixth magnitude. (Handwritten position added by Messier in his personal copy: 14h 40m, +56.).”

Even Pierre Mechain was vexed by the error and his letter to Bernoulli on May 6, 1783, he writes: “I will add only that No. 101 & 102 on the p. 267 of the Connoissance des tems [for] 1784 are nothing but the same nebula, which has been taken for two, by an error in the [sky] charts.” Later, Bode would find in his notes: “On page 267 of the “Connoissance des Temps for 1784″ M. Messier lists under No. 102 a nebula which I have discovered between Omicron [actually Theta] Bootis and Iota Draconis; this is a mistake. This nebula is the same as the preceding No. 101. Mr. Messier, caused by an error in the sky charts, has confused this one in the list of my nebulous stars communicated to him.” Although the positioning error occurred, the description was correct for NGC 5866.

It’s Messier designation will probably forever by the subject of debate, but even other notable astronomers called in errors on this one as well. Both Herschels observed it and even Admiral Smyth – who probably following an error by John Herschel in his 1833 catalog, confuses its number with H I.219 (which is NGC 3665, a galaxy in Ursa Major), and thus erroneously gives that object’s discovery date, March 1789: “A small but brightish nebula, on the belly of Draco, with four small stars spreading across the field, north of it. There may be a doubt as to whether this is the nebula discovered by Mechain in 1789, since Messier merely describes it as “very faint,” and situated between Omicron Bootis and Iota Draconis. But there must be some mistake here; the one being on the herdman’s leg, and the other in the coil of the Dragon far above the head of Bootes, having 22 deg of declination and 44′ [44 min] of time [in RA] between them, a space full of all descriptions of celestial objects. But as the Theta in the raised right hand of Bootes, if badly made, might be mistaken for an omicron, this is probably the object seen by Mechain, and JH’s 1910 [NGC 5879]; it being the brightest nebula of five in that vicinity [actually, the brightest is NGC 5866]. A line from Kappa in Draco’s tail, led to the south-east of Thuban, and prolonged as far again, strikes upon its site.”

Don’t you mistake the beautiful Spindle Galaxy for anything but a great observation!

Top M102 image credit, Palomar Observatory courtesy of Caltech, M102 Hubble Images, 2MASS M102 image, M102 data images by AANDA and M102 image courtesy of NOAO/AURA/NSF.

Object Name: Messier 101
Alternative Designations: M101, NGC 5457, Pinwheel Galaxy
Object Type: Type Sc Spiral Galaxy
Constellation: Ursa Major
Right Ascension: 14 : 03.2 (h:m)
Declination: +54 : 21 (deg:m))
Distance: 27000 (kly)
Visual Brightness: 7.9 (mag)
Apparent Dimension: 22.0 (arc min)

Locating Messier 101: M101 is easily located by finding the first star (Eta) in the handle of the “Big Dipper” asterism in Ursa Major. It lays almost exactly the same distance north as the distance between Eta and the second star in the handle -Zeta. Simply form a mental triangle with the northern apex as your target position. From a good dark sky site, M101 can be spotted with larger binoculars as a vague, misty round patch – but doesn’t become apparent as a bright nucleus galaxy without the aid of a mid-sized telescope and show spiral structure to large aperture. Be aware that the outer edges are very vague and glimpses of patchy outside structure are actually star forming regions on Messier 101’s periphery. While the galaxy can be spotted under less than perfect sky conditions, it does require a good, dark night for serious study.

What You Are Looking At: At roughly 27 million light years away and spanning over 170,000 light years, Messier 101 is one of the biggest disc galaxies known so far. Shining with the light of about 30 billion suns, the Pinwheel galaxy is known as one of the most prominent Grand Design spiral galaxies in the sky – even if it is just a little lopsided… lopsided enough that Halton Arp has included M101 as No. 26 in his Catalogue of Peculiar Galaxies as a “Spiral with One Heavy Arm”. Why? Maybe because its interacting. According to Teresa Grabinska and Mirosaw Zabierowski; “We discuss Arp’s hypothesis that the HII regions are more numerous and more conspicuous on the side of a galaxy facing its companion. Arp’s hypothesis seems not to be true if we add to Hodge’s sets of galaxies only the most probably tidally-interacting cases.”

However, things get really interesting when we look at M101 with X-ray eyes. According to the work of Massimo Persic and Yoel Rephaeli: “Young galactic X-ray point sources (XPs) closely trace the ongoing star formation in galaxies… (The) relation provides the most adequate X-ray estimator of instantaneous SFR by the phenomena characterizing massive stars from their birth (FIR emission from placental dust clouds) through their death as compact remnants (emitting X-rays by accreting from a close donor).

Of course, all this activity means an increase in supernovae, doesn’t it? Darn right. “A new multiepoch Ha imaging study of M101 (NGC 5457) has been carried out as part of a larger campaign to study the rate and stellar population of extragalactic novae. The survey yielded a total of 13 nova detections from 10 epochs of M101 observations spanning a 3 year period.” says E.A. Coelho (et al). “The spatial distribution of the combined nova sample from the present survey and from the earlier Shafter et al. survey shows that the specific frequency of novae closely follows the integrated background light of the galaxy.”

But there’s still plenty of mystery left to discover in Messier 101. “After a review of the discovery of external galaxies and the early classification of these enormous aggregates of stars into visually recognizable types, a new classification scheme is suggested based on a measurable physical quantity, the luminosity of the spheroidal component. It is argued that the new one-parameter scheme may correlate well both with existing descriptive labels and with underlying physical reality. Two particular problems in extragalactic research are isolated as currently most fundamental. A significant fraction of the energy emitted by active galaxies (approximately 1% of all galaxies) is emitted by very small central regions largely in parts of the spectrum (microwave, infrared, ultraviolet and x-ray wavelengths) that were previously inaccessible to observation.” says J.P. Ostricker.

“The physical processes by which regions with the volume of the luminous stellar parts of galaxies produce such enormous quantities of energy are currently the subject of much speculative debate. It appears that most of the mass of ordinary galaxies resides far from the central luminous region, with the volume containing most of this mass times the volume containing most of the light-emitting stars; the nature, amount, and extent of this mass are quite unknown. New instruments that will be operating in the next decade and that may be helpful in solving these two problems are briefly mentioned with particular emphasis on the advances expected in angular resolution at wavelengths for which picture-taking ability has historically been poor or nonexistent.”

History: The Pinwheel Galaxy was discovered by Pierre Mechain on March 27, 1781, and added as one of the last entries in Charles Messier’s catalog as M101. Messier writes: “Nebula without star, very obscure and pretty large, of 6 or 7 minutes [of arc] in diameter, between the left hand of Bootes and the tail of the great Bear [Ursa Major]. It is difficult to distinguish when one lits the [graticule] wires.”

It would be Sir William Herschel who would shatter it into structure in 1783 when he writes in his unpublished notes: ” In the northern part is a large [bright] star pretty distinctly seen, and in the southern I saw 5 or 6 small [faint] ones glitter through the greatest nebulosity which appears to consist of stars. Evening bad. This and the 51st [M51] are both so far removed from the appearance of stars that it is the next step to not being able to resolve them. My new 20 feet will probably render it easy. On 1789, April 14 (Sw. 921). vB. SN. [very bright, small nucleus] with extensive nebulosity, pretty well determined on the preceding [W] side, but very diffuse to the north following [NE]. Includes the two following nebulae [III.788 and 789, NGCs 5461, 5462], and seems to extend 20′, perhaps 30′ or more.” Little did he know at the time he was actually picking up star forming regions!

However, by 1837 Admiral Smyth was beginning to get a clue. Says he: “This object was discovered by Mechain in 1781, in whose instruments it was very obscure; and it only exhibited a mottled nebulosity to WH [William Herschel]. Under a very favourable view it is large and well spread, though somewhat faint except towards the center, where it brightens. There are several telescopic stars in the field, one of which is very close to the nebula. From the nature of this neighborhood, and a trifling uncertainty in the earlier data, this object may be 214 H I [this is actually NGC 5474]; but that astronomer does not appear to have been aware of the identity. It is one of those globular nebulae that seem to be caused by a vast agglomeration of stars, rather than by a mass of diffused luminous matter; and though the idea of too dense a crowd may intrude, yet the paleness tells of its inconceivable distance, and probable discreteness.”

May you enjoy your 27 million light year journey into M101 as much!

Top M101 image credit, Palomar Observatory courtesy of Caltech, M101 Hubble Image, Messier 101 in UV by Ultraviolet Imaging Telescope (UIT and NASA), NASA’s Spitzer Space Telescope, Composite M101 as Viewed by Spitzer, Hubble and Chandra, Hubble B&W image and M101 image courtesy of George Jacoby, Bruce Bohannan, Mark Hanna/NOAO/AURA/NSF.

Object Name: Messier 100
Alternative Designations: M100, NGC 4321
Object Type: Type Sc Spiral Galaxy
Constellation: Coma Berenices
Right Ascension: 12 : 22.9 (h:m)
Declination: +15 : 49 (deg:m)
Distance: 60000 (kly)
Visual Brightness: 9.3 (mag)
Apparent Dimension: 7×6 (arc min)

Locating Messier 100: As part of the Virgo Cluster of Galaxies, M100 is best found by returning to our “galaxy hopping” ways we’ve learned. Begin with the bright M84/84 pairing located in the heavily populated inner core of the Virgo Cluster of galaxies about halfway between Epsilon Virginis and Beta Leonis. Once identified, stay at the eyepiece a move your telescope north until you locate M99 and continue at least 3 or 4 more eyepiece fields. This is what is known as “sweeping”. When you reach a star pattern you are certain that you can identify, shift the telescope one eyepiece field to the east and continue northward for several eyepiece fields. If you have not seen the fairly large round patch of M100, continue the process carefully one eyepiece field at a time. (Not all eyepieces have the same apparent field of view, but use your lowest magnification.) M100 is face-on in presentation, so it will be a round of nebulousity that requires dark, clear skies and can be spotted with binoculars.

What You Are Looking At: M100 is a spiral galaxy, very similar to our own Milky Way. The galaxy has two distinct arms of young, hot and massive stars which show photographically as bright blue stars. These stars have formed recently from interactions with neighboring galaxies, but in a slightly odd way. “The total H I distribution is mostly confined to the radius of the optical disk, but a large though faint extension is seen in the H I data at 45” resolution on the SW side of the disk. NGC 4321 is asymmetric in H I and may be called “lopsided.” We have derived a rotation curve which agrees fairly well with what was previously published but shows more detail due to the higher resolution of our new observations. The rotation curve does not decline within the radius of the disk, but important differences are seen between the behavior of the approaching and the receding sides.” says Johan H. Knapen (et al), “These differences are caused by deviations from circular motions in the outer disk that are probably due to a close passage of the companion galaxy NGC 4322, which may also be the cause of the observed asymmetry in the total H I distribution. Deviations from circular motion due to density wave streaming are seen in the inner disk. From skewing of the velocity contours in the central part of NGC 4321, the presence of a nonaxisymmetric potential is deduced. Near-infrared and H? images indicate that a bar is indeed present in this galaxy. The deviations from circular motions seen in the velocity field can be identified with gas streaming around the bar in elongated orbits, in broad agreement with theoretical predictions.”

As one of Lord Rosse’s original 14 “spiral nebula”, Messier 100 seems to employ a perfect spiral shape – one that seems to lack a central bar structure. “We analyse new integral-field spectroscopy of the inner region (central 2.5 kpc) of the spiral galaxy NGC 4321 to study the peculiar kinematics of this region. Fourier analysis of the velocity residuals obtained by subtracting an axisymmetric rotation model from the H? velocity field indicates that the distortions are global features generated by an m= 2 perturbation of the gravitational potential which can be explained by the nuclear bar.” says A. Castillo-Morales (et al). “This bar has been previously observed in the near-infrared but not in the optical continuum dominated by star formation. We detect the optical counterpart of this bar in the 2D distribution of the old stellar population (inferred from the equivalent width map of the stellar absorption lines). We apply the Tremaine–Weinberg method to the stellar velocity field to calculate the pattern speed of the inner bar, obtaining a value of ?b= 160 ± 70 km s?1 kpc?1 . This value is considerably larger than the one obtained when a simple bar model is considered. However, the uncertainties in the pattern speed determination prevent us from giving support to alternative scenarios.”

To study M100 is to take a look back into its growth and history… a history that apparently isn’t “going quietly into that good night”. Astronomers are still able to observe the remains of a star which exploded in 1979 – still shining as brightly in X-rays now as when it was first observed. This in itself is unusual because most supernova events fade fairly quickly in a period of just a few months. Dr. Stefan Immler at NASA’s Goddard Space Flight Center in Greenbelt, Md., led this observation using the European Space Agency’s XMM-Newton observatory. The star explosion (supernova), called SN 1979C, shows no sign of letting up, he said. By observing with the XMM-Newton optical/UV image of the galaxy M100 and supernova SN 1979C obtained with the Optical Monitor in the B, U, and UVW1 filters we’ve taken one of our deepest looks ever. The position of SN 1979C is marked by a white circle. The streak across the image is from an artifact caused by a dead detector column. The scale bar is 2 arc min, corresponding to 32,600 light years.

“This 25-year-old candle in the night has allowed us to study aspects of a star explosion never before seen in such detail,” Immler said. “All the important information that usually fades away in a couple of months is still there.” Among the many unique finds, Immler said, is the history of the star’s stellar wind dating back 16,000 years before the explosion. Such a history is not even known about our Sun. Also, the scientists could measure the density of the material around the star, another first. The lingering mystery, though, is how this star could fade away in visible light yet remain so radiant in X-rays. The results appear in The Astrophysical Journal. How is this accomplished? Through a composite XMM-Newton X-ray image of the galaxy M100 in soft (0.3-1.5 keV, red), medium (1.5-4 keV, green) and hard (4-10 keV, blue) X-rays. The image shows large amounts of diffuse X-ray emission from hot gas in the galaxy (red), various point-like X-ray sources and supernova SN 1979C south-east of the nucleus of M100 (marked by a white line). “We can use the X-ray light from SN 1979C as a ‘time machine’ to study the life of a dead star long before it exploded,” Immler said.

History: Messier 100 was originally discovered by Pierre Mechain on March 15, 1781. It was later confirmed and cataloged by Charles Messier on April 13, 1781 who wrote in his notes: “Nebula without star, of the same light as the preceding [M99], situated in the ear of Virgo. Seen by M. Mechain on March 15, 1781. The three nebulae, nos. 98, 99 & 100, are very difficult to recognize, because of the faintness of their light: one can observe them only in good weather, and near their passage of the Meridian.”

It would be observed and cataloged by both Herschels, but it was Admiral Smyth who described it the best: “A round nebula, pearly white, off the upper part of the Virgin’s left wing, and certainly at a great distance from Virgo’s ear of corn, where the Connaissance des Temps places it [actually Messier’s position is quite close]: indeed, the true site will be hit upon just one-fifth the way from Beta Leonis towards Arcturus. This is a large but pale objects, of little character, though it brightens from its attenuated edgestowards the centre; and is therefore proved to be globular. It was discovered by M. Méchain in 1781, and is accompanied by four small stars, at a little distance around it; besides minute points of light in the field, seen by occasional gleams.

We are now in the broad grand stratum of nebulae, which lies in a direction almost perpendicular to the Galaxy [Milky Way], and passes from the south, through Virgo, Berenices Hair, Canes Venatici, and te Great Bear, to the Pole, and beyond. This glorious but mysterious zone of diffused spots, is an indisputable memorial to all future times, of the unwearied industry and indomitable scientific energy of Sir William Herschel. Yet has this unrivaled contributor to knowledge been disparagingly described, as a man indulging in “speculations of no great value to astronomy, rather than engage in computations by which the science can really be benefited.” Save the mark! This is said of a philosopher of zeal and application hitherto unequaled: one whose contributions to the Philosophical Transactions prove the bold but circumspect grandeur of his conceptions, his consummate mechanical resources, and the exactness of his elaborate calculations. Herschel’s labor, however, transcended those of the ages in which he was cast, although he gave such animation and bias to sidereal astronomy that his mantle was caught at.”

May you, too, “save the mark”!

Top M100 image credit, Palomar Observatory courtesy of Caltech, M100 Hubble Image, Issac Newton Telescope True-color image of M100, M100 XMM Newton Images and M100 image courtesy of N.A.Sharp/NOAO/AURA/NSF.

Object Name: Messier 99
Alternative Designations: M99, NGC 4254, Pinwheel Galaxy
Object Type: Type Sc Spiral Galaxy
Constellation: Coma Berenices
Right Ascension: 12 : 18.8 (h:m)
Declination: +14 : 25 (deg:m)
Distance: 60000 (kly)
Visual Brightness: 9.9 (mag)
Apparent Dimension: 5.4×4.8 (arc min)

Locating Messier 99: As part of the Virgo Cluster of Galaxies, M98 is best found by returning to our “galaxy hopping” ways we’ve learned. Begin with the bright M84/84 pairing located in the heavily populated inner core of the Virgo Cluster of galaxies about halfway between Epsilon Virginis and Beta Leonis. Once identified, stay at the eyepiece a move your telescope north until you locate M99. This face-on presentation will look like a round hazy patch to small optics and begin revealing its spiral arm pattern with mid-sized telescopes under dark skies.

What You Are Looking At: What’s in an Sc designation when it comes to a spiral galaxy? It means its rotating counterclock-wise. While that sounds very normal, you’ll also notice that M99’s mass seems to be just a little “off center”. What’s going on here? Let’s turn to the research of Victor P. Debattista and J. A. Sellwood: “We show that bars in galaxy models having halos of moderate density and a variety of velocity distributions all experience a strong drag from dynamical friction unless the halo has large angular momentum in the same sense as the disk. The frictional drag decreases the bar pattern speed, driving the co-rotation point out to distances well in excess of those estimated in barred galaxies. The halo angular momentum required to avoid strong braking is unrealistically large, even when rotation is confined to the inner halo only. We conclude, therefore, that bars are able to maintain their observed high pattern speeds only if the halo has a central density low enough for the disk to provide most of the central attraction in the inner galaxy. We present evidence that this conclusion holds for all bright galaxies.”

But what if it wasn’t just the galaxy itself, but a chance merger? “We present high-resolution H I and H? observations of the spiral galaxy NGC 4254. The observations were obtained with the VLA and the Maryland-Caltech Fabry-Perot camera, respectively. NGC 4254 is unusual in having a grand-design spiral structure with a strong m = 1 component for which there is no obvious cause in optical images. Our observations reveal that, in addition to the usual galactic disk component, there are H I clouds superposed on and beyond the H I disk, at velocities up to 150 km s^-1^ from those established for the disk. The mass in these clouds is ~2.3 x 10^8^ M_sun_, and they may be the remnants of an entity that was tidally disrupted by NGC 4254 and is now merging with it. The direct effects of the interaction between the cloud gas and the galaxy are limited to the region where the gas appears to be merging with the disk, where it may be causing a warp.” says Yuichi Terashima (et al).

“But the indirect effects of the infalling gas appear profound: it is the most likely cause for the unusual spiral structure of NGC 4254. If so, the m = 1 spiral structure of NGC 4254 is recent, and an internal amplification mechanism such as swing amplification has played a major role in its evolution. Since NGC 4254 does not appear to be exceptionally deficient in dark matter and is apparently a normal Sc galaxy, the nature of the interaction appears important in determining the susceptibility of the disk to various spiral modes (in particular the m = 1,3, and 5 modes of NGC 4254).”

Spiral modes, huh? T. Kranz (et al) knows a lot about that, and before there can be stars there has to be the material to make them – gas. “As a pilot project, we analyzed the data of NGC 4254 (M99). Assuming a constant stellar mass to light ratio, the gravitational potential due to the stellar mass fraction was calculated by direct integration over the whole mass distribution taken from the NIR-image. The mass to light ratio for the maximum disk contribution was scaled by the measured rotation curve. For the dark matter contribution we assumed an isothermal halo with a core. To combine the two components we chose a stellar mass fraction and added the halo with the variable parameters adjusted to give a best fit to the rotation curve.” says Kranz, “We used this potential as an input for the hydrodynamical gas simulations. Figure 2 presents the results for the resulting gas surface density, as it settles in the potenital. The morphology of the gas distribution is very sensitive to the velocity, with which the spiral pattern of the galaxy rotates (pattern speed).”

“Determining individual mass fractions of the luminous and dark matter is not a straightforward task. The rotation curve of a disk galaxy is only sensitive to the total amount of gravitating matter, but does not allow to distinguish the two mass density profiles,” continues Kranz. “Here we would like to exploit the fact, that the stellar mass in disk galaxies is often organized in spiral arms, thus in clearly non-axisymmetric structures.”

“On the other hand, in most proposed scenarios, the dark matter is non-collisional and dominated by random motions. It is not susceptible to spiral structures and distributed like the stars in elliptical galaxies. If the stellar mass dominates, the arms could induce considerable non-circular motions in the gas, which should become visible as velocity wiggles in observed gas kinematics. Using hydrodynamical gas simulations we are able to predict these velocity wiggles and compare them to the observations. Hence the contribution of the perturbative forces with respect to the total forces can be determined quantitatively and can be used to constrain the disk to halo mass ratio.”

History: M99 was discovered on March 15, 1781 by Messier’s colleague and friend, Pierre Mechain, together with the nearby situated M98 and M100. Charles Messier measured its position and included it in his catalog on April 13, 1781. In his notes he writes: “Nebula without star, of a very pale light, nevertheless a little clearer than the preceding [M98], situated on the northern wing of Virgo, and near the same star, no. 6, of Comae Berenices. The nebula is between two stars of seventh and of eighth magnitude. M. Mechain saw it on March 15, 1781.”

While M99 would be observed by both William and John Herschel, it would be Lord Rosse who finally brought it to light. Even though he didn’t truly understand the nature of what he was looking at, he was fascinated with knowing it had a spiral structure and M99 became his second “confirmed kill”. In his notes he writes: “In the following spring [of 1846] an arrangement, also spiral but of a different character [than in M51], was detected in 99 Messier, Plate XXXV. fig 2. This object is also easily seen, and probably a smaller instrument, under favourable circumstances, would show everything in the sketch.”

Top M99 image credit, Palomar Observatory courtesy of Caltech, M99 2MASS image, M99 by Hunter Wilson, M99 Spitzer images, M99 courtesy of Ole Nielsen, Rosse’s historical M99 sketch and M99 image courtesy of NOAO/AURA/NSF.