Artikel zu "The Whirlpool Galaxy (M51 = NGC 5194 und NGC 5195)"

M51

M16: The Eagle Nebula
SN 1994I in M51
SN 2005cs in M51
K1 M51 (NGC 5194): The Whirlpool Galaxy
K2 ULXs: Ultra-luminous X-ray Objects
K3 M51 (NGC 5194): The Whirlpool Galaxy — Info —
VLA: SN 1994I
K4 Simulation: M51 and M101 at high redshift
K5 Hubble Reveals the Heart of the Whirlpool Galaxy
K6 M51 as observed by SDSS, Spitzer, GALEX and HST
K7 The Star Cluster Population of M51
K8 Gas Clouds Yield Important Clues Supporting Theory on Spiral Arms
K9 Out of This Whirl: the Whirlpool Galaxy (M51) and Companion Galaxy
Literatur

The Whirlpool Galaxy was discovered by the French comet-hunter Charles Messier on October 13, 1773.
He included it as object number 51 in his now-famous catalog of astronomical objects that, in a small telescope, might be mistaken for a comet.
In 1845, the British astronomer Lord Rosse discovered the spiral structure in the galaxy.

M51: The Whirlpool Galaxy (NGC 5194)

K1 M51 (NGC 5194): The Whirlpool Galaxy

Credit: W. Keel (U. Alabama; January 25, 1997)

M51: The Whirlpool Galaxy (NGC 5194)
1.1-meter Hall Telescope, Lowell Observatory

ESO / ISOCAM

Reprocessed ISOCAM image of M51

Explanation:
The Whirlpool Galaxy is a classic spiral galaxy. At only 7.7 Mpc distant, M51, also cataloged as NGC 5194, is one of the brighter and more picturesque galaxies on the sky. The smaller galaxy appearing here above and to the right is also well behind M51, as can be inferred by the dust in M51's spiral arm blocking light from this smaller galaxy.
Astronomers speculate that M51's spiral structure is primarily due to it's gravitational interaction with this smaller galaxy.
X-ray observations also strongly suggest the presence of an AGN in M 51.

K2 ULXs: Ultra-luminous X-ray Objects

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	Authors: Ji-Feng Liu, Joel N. Bregman, Jimmy Irwin, Patrick Seitzer
	Journal-ref: ApJ 581 (2002) L93-L96 [astro-ph/0211311 ]
	Title: An Ultra-luminous X-Ray Object with a 2 hour period in M51
Abstract: Ultra-luminous X-Ray Objects are off-nucleus point sources with L_X=10³⁹-10⁴¹ ergs s^-1 but the nature of such systems are largely unidentified. Here we report a 2.1 hour period observed in a Chandra ACIS observation for ULX M51 X-7, which is located on the edge of a young star cluster in the star forming region in a spiral arm. In two ACIS observations separated by one year, the ULX changed from a high-hard to a low-soft spectral state, in contrast to most Galactic low mass X-ray binaries. Based on its period and spectral behaviors, we suggest that this ULX is a low mass X-ray binary system, with a dwarf companion of 0.2-0.3 M and a compact accretor, either a neutron star or a black hole, whose mass is not well constrained. Relativistic beaming effects are likely involved to produce the observed high X-ray luminosities given its low accretion rate as inferred from a sustainable accretion scenario via Roche lobe overflow. 1. Introduction X-ray emission from active galactic nuclei and quasars, powered by accretion onto nuclear super-massive black holes, are usually L_X > 10⁴¹ erg ^-1, while for the stellar binary systems in the Milky Way, the luminosities are typically L_X = 10³³-10³⁸ ergs s^-1. X-ray objects with luminosities of L_X=10³⁹-10⁴¹ ergs s^-1 have been observed in some external galaxies as off-nucleus point sources by X-ray satellites such as EINSTEIN, ROSAT, ASCA, and recently Chandra X-ray Observatory. These objects have several names, a popular designation being Ultra-luminous X-ray Objects, or ULXs.

ESO / XMM

Fig. 1.— Left: Three color image of M 51 created from adoptively smooth XMM-Newton EPIC PN images. The three colors red, green, and blue correspond to the 0.2-0.7 keV, 0.7-2 keV, and 2-10 keV energy bands. North is towards the top and east is to the left of the image. The extended source at the top of the image is the companion galaxy NGC 5195. The bright extended source near the center of the image is the center of the galaxy NGC 5194 that consists of extended soft emission and two hard X-ray sources: the LLAGN and an ULX NGC 5194 source 26. Right: The EPIC PN image of M 51 in the 2-10 keV band showing the positions of 9 ULXs and the LLAGN.

One suggestion for the nature of these ULXs is that they are binary systems with 10³-10⁴ M black holes as primaries (Colbert and Mushotzky 1999). Such black holes, if they exist, are the missing links between stellar mass black holes and super-massive black holes in the nuclei of galaxies. This suggestion is consistent with the X-ray spectral of some ULXs (Makishima et al. 2000). However, the formation of such massive black holes is not predicted by stellar evolution theory and it may be impossible to form such objects even in dense star clusters. Alternatively, these sources may be stellar mass black holes or neutron stars whose emission is beamed, thereby representing micro-quasars. If the emission is beamed, the intrinsic luminosities become sub-Eddington, and there are known examples of beamed Galactic X-ray sources.
It is also possible that the luminosities are truly super-Eddington, for example, obtainable from accretion disks with radiation-driven inhomogeneities.
To identify which of the above suggestions is correct, one natural and fruitful way is to associate them with known classes of objects by comparing spectral behaviors, short-term and long-term variabilities, etc. Spectral analyses of ULXs, not without problems, generally support the mass-accreting black hole scenarios. Spectral transitions were observed for two ULXs in IC 342 between high-soft and low-hard states, reminiscent of some black hole X-ray binaries in our Galaxy. While many ULXs are variable during individual observations, few periods have been reported. So far, only a possible periodicity at several tens of hours of a ULX in IC 342 has been reported.

In this paper, we report a 2.1 hour period for a ULX in M51 (NGC 5194), M51 X-7 as designated in Roberts & Warwick 2000. This ULX is located on the outskirts of a young open cluster on a spiral arm of M51.
A period of 7620 seconds for the ULX is found from the X-ray light, and a spectral transition is found between two Chandra observations. We discuss the implications of its period and spectral evolution, and suggest that this ULX is a low mass X-ray binary system, with a dwarf companion of 0.2-0.3 M and a compact accretor. Possible mechanisms to produce the high X-ray luminosity is also discussed. For the distance to M51, we use 7.7 Mpc.

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	Authors: Gulab C. Dewangan, Richard E. Griffiths, Manojendu Choudhury, Takamitsu Miyaji, Nicholas J. Schurch
	Journal-ref: ApJ 635 (2005) 198-213 [astro-ph/0508431 ]
	Title: XMM-Newton view of the ultra-luminous X-ray sources in M51
Abstract: We present results based on XMM-Newton observation of the nearby spiral galaxy M51 (NGC5194 and NGC5195). Two ULXs in NGC5194 show evidence for short-term variability, and all but two ULXs vary on long time scales (over a baseline of 2.5 years), providing strong evidence that these are accreting sources. One ULX in NGC5194, source 69, shows possible periodic behavior in its X-ray flux. We derive a period of 5925 ± 200 s at a confidence level of 95%, based on three cycles. This period is lower than the period of 7620 ± 500 s derived from a Chandra observation in 2000. The higher effective area of XMM-Newton enables us to identify multiple components in the spectra of ULXs. Most ULXs require at least two components -- a power law and a soft X-ray excess component which is modeled by an optically thin plasma or multicolor disk blackbody (MCD). However, the soft excess emission, inferred from all ULXs except source 69, are unlikely to be physically associated with the ULXs as their strengths are comparable to that of the surrounding diffuse emission. The soft excess emission of source 69 is well described either by a two temperature mekal plasma or a single temperature mekal plasma kT~690eV) and an MCD (kT~170eV). The MCD component suggests a cooler accretion disks compared to that in Galactic X-ray binaries and consistent with that expected for intermediate mass black holes (IMBHs). An iron K_a line (EW ~ 700eV) or K absorption edge at 7.1keV is present in the EPIC PN spectrum of source 26. The spectrum of the ULX in NGC5195, source 12, is consistent with a simple power law. The LLAGN in NGC 5194 shows an extremely flat hard X-ray power-law (G ~ 0.7), a narrow iron K line at 6.4 keV (EW ~ 3 keV), and strong soft X-ray excess emission. The full band spectrum is well described by a two component mekal plasma and reflection from cold material such as putative torus.

M 51, also known as the Whirlpool galaxy, is a faceon spiral galaxy and is located at a distance of 8.4 Mpc. Optical studies of emission lines classified it as a LINER or a Seyfert 2 galaxy. Furthermore, Ho et al. (1997) suggest the presence of a broad H_a line. Kohno et al. (1996) found a nuclear molecular disk, and constrained the dynamical mass within 70 pc of the nucleus to be 4 - 7 × 10⁶M. This indicates that M 51 hosts as massive a black hole as many AGNs.

ESO / XMM

Fig. 2.— XMM-Newton ultra-violet image overlaid with the 1.5-10 keV band X-ray contours, derived from the PN image, showing the discrete hard X-ray sources. The contours are drawn at levels of 0.4, 0.7, 1.3, 1.9, and 2.6 counts pixel-2 (1 pixel = 0.953 arcsec). The image size 11.1' × 11.1'. North is up and east is left. Two central hard X-ray sources, about 20'' apart, are clearly resolved by the EPIC instruments. The center of UV image coincides with the fainter of the two hard X-ray sources in the central regions. This fainter source is the LLAGN in NGC 5194. The brighter source is the ULX NGC 5194 source 26.

X-ray observations also strongly suggest the presence of an AGN in M 51. Einstein and ROSAT observations constrained the soft X-ray luminosity of the M 51 nucleus to be L_X < 5 × 10³⁹ erg s^-1. Ginga scanning observations in 1988 detected bright hard X-ray emission with 2 - 20 keV luminosity of ~ 1.2 × 10⁴¹ erg s^-1, a photon index of 1.43 ± 0.08 and an intrinsic absorption of < 7 × 10²¹ cm^-2. Such hard nuclear X-ray emission is often considered to be evidence for a low luminosity AGN (LLAGN). ASCA observed M 51 in the hard (2 - 10 keV) X-ray band in 1993, and did not detect such a bright hard component.

Instead, a faint hard X-ray continuum with a neutral Fe K_a line was detected, whose flux was an order of magnitude lower than that measured by Ginga. The reason for this large difference in luminosity has recently been clarified by BeppoSAX observations. Fukazawa et al. (2001) find that the nucleus is photoelectrically absorbed below 10 keV but is observed directly above 20 keV, implying an absorbing column of N_H ~ 5.6 × 10²⁴ cm^-2. The 2-10 keV luminosity measured by BeppoSAX was similar to that of ASCA. Fukazawa et al. (2001) attributed the higher Ginga luminosity to variability of the absorbing column.
High angular resolution ROSAT HRI observations also revealed eight X-ray point sources and diffuse soft X-ray emission in M 51. Chandra observed M 51 during June 2000 and June 2001 with ACIS-S.

The X-ray image revealed the nucleus, 113 X-ray sources and extended emission which resembled the morphology of both the radio and optical emission line images. The X-ray image of the nucleus is well represented by a model consisting of soft thermal plasma (kT ~ 0.5 keV), a very hard continuum and an Fe K_a emission line at 6.45 keV with an equivalent width of greater than 2 keV. The X-ray spectra of the extra-nuclear clouds are well fitted by a thermal plasma model with kT ~ 0.5 keV.

The spectral shape and morphology strongly suggest that the clouds are shock-heated by a bipolar outflow from the nucleus. Out of 113 extra-nuclear sources, 9 sources have luminosities exceeding 10³⁹ erg s^-1 in the 0.5-8 keV band. The number of extra-nuclear sources in M 51 is much higher than in most other normal spiral and elliptical galaxies and is similar to galaxies experiencing star-burst activity. The X-ray spectra of most of the detected sources are consistent with a power-law spectral form with a photon index between 1 and 2, while one source has an extremely hard spectrum and two sources have particularly soft spectra. The X-ray spectra of three of the ULXs are consistent with both a power-law and multi-color blackbody model. One ULX showed a remarkable spectrum with prominent emission lines.

K3 M51 (NGC 5194): The Whirlpool Galaxy

— Info —

M51 und Begleiter NGC 5195. Die Whirlpool-Galaxie in den JAGDHUNDEN hat Magnitude m = 8.4

Im Jahr 1994 wurde von den Amateur Astronomen Jerry Armstrong und Tim Puckett (aus Atlanta, USA) eine Supernova (1994I Typ Ic) in M51 entdeckt.

Die berühmte Whirlpool Galaxie M 51 war eine von Messier's eigenen Entdeckungen: Er fand sie am 13. Oktober 1773, als er einen Kometen beobachtete.

Der Begleiter, NGC 5195, wurde 1781 von seinem Freund Mechain entdeckt, so daß es 1784 in seinem Katalog wie folgt erwähnt wird:

`Es ist ein Doppel, jede hat ein helles Zentrum, die 4'35" voneinander entfernt sind. Die beiden "Atmosphähren" berühren einander, eine ist schwächer als die andere.'

M 51 ist das dominierende Mitglied einer kleinen Gruppe von Galaxien. Da sie 37 Millionen Lichtjahre entfernt und dennoch so deutlich sichtbar ist, muß es sich bei ihr in der Tat um eine große und leuchtkräftige Galaxie handeln.

Diese Galaxie war die erste, bei der eine Spiralstruktur entdeckt worden ist (im Jahre 1845 von Lord Rosse, der eine sehr sorgfältige und genaue Zeichnung anfertigte).

Supernova 1994I was discovered on April 2, 1994 by amateur astronomers Jerry Armstrong and Tim Puckett of the Atlanta Astronomy Club. It got as bright as magnitued 12.8 and was classified as of type Ic.
Supernova 1994I was one of the brighter Sn from the recent past. Announced in IAUC 5961 this supernova was discovered independently by several people. 1994I was discovered in the magnitued 8.4 Whirlpool galaxy (aka M51, NGC 5194) in UMa. This supernova got as bright as magnitued 12.8.

— Compact Radio Sources in M51 —

VLA high-resolution observations — distance: d = 8.4 Mpc
	Authors: L.A. Maddox, J.J. Cowan, R.E. Kilgard, E. Schinnerer, C.J. Stockdale
	Journal-ref: AJ (2007) [astro-ph/0702310 ]
	Title: A Study of Compact Radio Sources in Nearby Face-on Spiral Galaxies. II. Multiwavelength Analyses of Sources in M51
Abstract: We report the analysis of deep radio observations of the interacting galaxy system M51 from the Very Large Array, with the goal of understanding the nature of the population of compact radio sources in nearby spiral galaxies. We detect 107 compact radio sources, 64% of which have optical counterparts in a deep H_a Hubble Space Telescope image. Thirteen of the radio sources have X-ray counterparts from a Chandra observation of M51. We find that six of the associated H_a sources are young supernova remnants with resolved shells. Most of the SNRs exhibit steep radio continuum spectral indices onsistent with synchrotron emission. We detect emission from the Type Ic SN 1994I nearly a decade after explosion: the emission (160 ± 22 µJy beam^-1 at 20 cm, 46 ± 11 µJy beam^-1 at 6cm, a=-1.02 ± 0.28) is consistent with light curve models for Type Ib/Ic supernovae. We detect X-ray emission from the supernova, however no optical counterpart is present. We report on the analysis of the Seyfert 2 nucleus in this galaxy, including the evidence for bipolar outflows from the central black hole. The M51a/b interacting system has played host to three supernovae (SNe) in modern times. SN 1945A occurred in M51b, while SN 1994I and SN 2005cs happened in M51a. We will report briefly on the radio emission of SN 1994I, the only supernova that we have detected in this galaxy with our radio observations. Fig. 2.— Three color optical image of M51 from HST/ACS. Image credit: Image Credit: NASA, ESA, S. Beckwith, and The Hubble Heritage Team (STScI/AURA). The crosses indicate the positions of the historical supernovae in the galaxy. Fig. 3.— I Band image of M51 with radio sources overlayed. We have opted to use the smoother I band image instead of the H_a image as a background, to illustrate the position of the radio sources with respect to the optical galaxy. The radio sources have been binned according to their spectral index: steep spectrum sources in red, flat spectrum sources in green, inverted spectrum sources in blue, and indeterminate flat/steep spectrum sources in yellow. Fig. 4.— Radio contours of 20 cm emission overlayed on an optical HST image of the central 3.7 kpc M51a. The position of SN 1994I is marked. VLA observations made in the B configuration, with a deconvolved beam of 1.''47 × 1.''13. The contour levels are 70, 98, 200, 280, 400, 560, 800, 1120, 1600, and 2240 µJy beam^-1. Fig. 8.— An enlargement of the nuclear region of M51. The colors represent X-ray emission, while the contours represent 6 cm radio emission. The smallest point-like feature in each image is ~ 1.0''. The radio contour levels are 70, 98, 200, 280, 400, 560 and 800 µJy beam^-1.

K4 Simulation: M51 and M101 at high redshift

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Author: W. L. Freedman

Journal-ref: Int.J.Mod.Phys. A17S1 (2002) 58-69 [astro-ph/0202006

]

Title: The Measure of Cosmological Parameters

Abstract: New, large, ground and space telescopes are contributing to an exciting and rapid period of growth in observational cosmology. The subject is now far from its earlier days of being data-starved and unconstrained, and new data are fueling a healthy interplay between observations and experiment and theory. I briefly review here the status of measurements of a number of quantities of interest in cosmology: the Hubble constant, the total mass-energy density, the matter density, the cosmological constant or dark energy component, and the total optical background light.

Simulation: M51 and M101 observed at successively higher redshifts
Image credit: Kuchinski et al.		The Figure (from Kuchinski et al.) illustrates directly how the well-known Messier objects, M51 and M101 would appear when observed at successively higher redshifts. Corrections for redshift and surface--brightness dimming are applied to rest--frame ultraviolet (U--band and 1500 Angstrom) images. Only the highest surface--brightness features remain visible at high redshift, and these reasonably bright (as well as all fainter) galaxies will be missed in deep galaxy surveys. Top panel: (Left) Ground-based U-band (3500 Angstrom) image of M51. (Center) M51 artificially redshifted to z=0.6, corresponding to the HSTWFPC2 606W filter. (Right) M51 artificially redshifted to z= 1.2, corresponding to the HSTWFPC2 814W filter. Bottom panel: (Left) UIT far-ultraviolet (1500 Angstrom) image of M101. (Right) Simulated images of M101 at redshifts where the rest-frame UIT filter bandpass would coincide with the four HST WFPC2 filters used to image the Hubble Deep Field.

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	Authors: L. E. Kuchinski, B. F. Madore, W. L. Freedman & M. Trewella
	Journal-ref: AJ 122 (2001) 729 [astro-ph/0106454 ]
	Title: Quantitative Morphology of Galaxies Observed in the Ultraviolet
Abstract: We present a quantitative study of the far-ultraviolet (FUV) and optical morphology in 32 nearby galaxies and estimate the ``morphological k-correction'' expected if these objects were observed unevolved at high redshift. Using the common indices of central concentration (C) and rotational asymmetry (A) to quantify morphology, we consider independently two phenomena that give rise to this k-correction. Bandshifting, the decrease in rest-frame wavelength of light observed through optical filters, is explored by measuring these indices in several passbands for each galaxy, and it is found to be the primary driver of changes in C and A. In general, the optical trend found for decreasing C and increasing A when going to shorter wavelengths extends to the FUV. However, the patchy nature of recent star-formation in late-type galaxies, which is accentuated in the FUV, results in poor quantitative correspondence between morphologies determined in the optical and FUV. We then artificially redshift our FUV images into the Hubble Deep Field (HDF) filters to simulate various cosmological distance effects such as surface brightness dimming and loss of spatial resolution. Hubble types of many galaxies in our sample are not readily identifiable at redshifts beyond z ~ 1, and the galaxies themselves are difficult to detect beyond z ~ 3. Only features of the highest surface brightness remain visible at cosmological distances. Our simulations suggest that k-corrections alone are indeed capable of producing the peculiar morphologies observed at high redshift.

K5 Hubble Reveals the Heart of the Whirlpool Galaxy

Whirlpool-Galaxie

[April 5, 2001]

New pictures from the Hubble telescope are giving astronomers a detailed view of the Whirlpool galaxy's spiral arms and dust clouds, which are the birth sites of massive and luminous stars. This galaxy, also called M51 or NGC 5194, is having a close encounter with a nearby companion galaxy, NGC 5195, just off the upper edge of this image.

The companion's gravitational influence is triggering star formation in the Whirlpool, as seen by the numerous clusters of bright, young stars [highlighted in red].

Image Credit: NASA and The Hubble Heritage Team (STScI AURA)
Acknowledgment: N. Scoville (Caltech) and T. Rector (NOAO)

Whirlpool-Galaxie M51:
Ohne Frage eines der fotogensten Objekte, das "Hubble" je ablichtete. Die Galaxie wurde auch von der Erde aus oft fotografiert, aus dem All gelang der schönste Schnappschuss.

K6 M51 as observed by SDSS, Spitzer, GALEX and HST

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	Authors: D. Calzetti, R.C. Kennicutt, L. Bianchi, D.A. Thilker, D.A. Dale, C.W. Engelbracht, C. Leitherer, M.J. Meyer, M.L. Sosey, M. Mutchler, M.W. Regan, M.D. Thornley, L. Armus, G.J. Bendo, S. Boissier, A. Boselli, B.T. Draine, K.D. Gordon, G. Helou, D.J. Hollenbach, L. Kewley, B.F. Madore, D.C. Martin, E.J. Murphy, G.H. Rieke, M.J. Rieke, H. Roussel, K. Sheth, J.D. Smith, F. Walter, B.A. White, S. Yi, N.Z. Scoville, M. Polletta, D. Lindler
	Journal-ref: ApJ 633 (2005) 871-893 [astro-ph/0507427 ]
	Title: Star Formation in NGC5194 (M51a): The Panchromatic View from GALEX to Spitzer
Abstract: Far ultraviolet to far infrared images of the nearby galaxy NGC5194, from Spitzer, GALEX, Hubble Space Telescope and ground--based data, are used to investigate local and global star formation, and the impact of dust extinction in HII-emitting knots. In the IR/UV-UV color plane, the NGC5194 HII knots show the same trend observed for normal star-forming galaxies, having a much larger dispersion than starburst galaxies. We identify the dispersion as due to the UV emission predominantly tracing the evolved, non-ionizing stellar population, up to ages 50-100 Myr. While in starbursts the UV light traces the current SFR, in NGC5194 it traces a combination of current and recent-past SFR. Unlike the UV emission, the monochromatic 24 micron luminosity is an accurate local SFR tracer for the HII knots in NGC5194; this suggests that the 24 micron emission carriers are mainly heated by the young, ionizing stars. However, preliminary results show that the ratio of the 24 micron emission to the SFR varies by a factor of a few from galaxy to galaxy. While also correlated with star formation, the 8 micron emission is not directly proportional to the number of ionizing photons. This confirms earlier suggestions that the carriers of the 8 micron emission are heated by more than one mechanism.

1. Introduction
Over the past decade, discoveries of galaxy populations at earlier and earlier cosmic times has rekindled interest in star formation rate (SFR) indicators, estimated from a variety of monochromatic and non–monochromatic emission measurements across the full spectrum.
Of particular interest for cosmological studies are indicators exploiting measurements at restframe ultraviolet (UV), optical, and mid/far–infrared (MIR/FIR) wavelengths; the interest has, however, accompanied a renewed awareness that potential limitations are not fully quantified yet. Presence of even small amounts of dust extinction in the early galaxies hampers significantly SFR measurements from the rest-frame UV emission of the high–redshift galaxies (e.g., the Lyman-break galaxies).
The issue lays in how well tracers at each wavelength can measure the actual SFR. The main problem afflicting UV and optical SFR indicators is dust obscuration. There are two aspects to this problem. One is that regions with moderate amounts of dust will be dimmed in a way that depends not only on the amount of dust, but also on the distribution of the emitters relative to the absorbers. This problem is exacerbated by the fact that populations of different ages suffer different amounts of dust extinction. Recently it has been shown that quiescently star forming galaxies follow a different dust opacity–reddening relation than starburst galaxies

Spitzer, GALEX and HST

Fig. 1.a— The far–UV (blue), continuum–subtracted H_a (green), and 24 µm dust (red) emission of the galaxy pair.
North is up, East is left. The size of the pictures is 8'.6×11'.8.

Spitzer, GALEX and HST

Fig. 1.b— The continuum–subtracted H_a (blue), 3.6 µm stellar continuum (green), and 8 µm dust (red) emission of the galaxy pair.

Fig. 1.— Two three–color composites of M51.
The FUV and FIR images, from GALEX and Spitzer, respectively, have closely–matched resolution (~6'', while the resolution of the ground–based H_a image has been degraded to match that of the two space–borne images.

Fig. 2.— This second image exploits the higher angular resolution of the IRAC images (about 2'' FWHM) to provide higher level of detail. The stellar continuum emission traces evolved (old) stellar populations. In this figure, a foreground star appears pure green.

Pretty Objects as observed by SDSS [2004]
New pictures from the SDSS telescope. M51, the "Whirlpool" galaxy in the constellation Canes Venatici, is about 30 million light years [10Mpc] away from our galaxy (binned 4x4).

K7 The Star Cluster Population of M51

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	Authors: N. Bastian, M. Gieles, H.J.G.L.M. Lamers, R. de Grijs, R.A. Scheepmaker
	Journal-ref: A&A 431 (2004) 905
	Title: The Star Cluster Population of M51: II. Age distribution and relations among the derived parameters We use archival Hubble Space Telescope observations of broad-band images from the ultraviolet (F255W-filter) through the near infrared (NICMOS F160W-filter) to study the star cluster population of the interacting spiral galaxy M51. We obtain age, mass, extinction, and effective radius estimates for 1152 star clusters in a region of ~7.3 × 8.1 kpc centered on the nucleus and extending into the outer spiral arms. We find: i) that the cluster formation rate seems to have had a large increase ~50-70 Myr ago, which is coincident with the suggested second passage of its companion, NGC 5195, ii) a large number of extremely young (< 10 Myr) star clusters, which we interpret as a population of unbound clusters of which a large majority will disrupt within the next ~10 Myr, and iii) that the distribution of cluster sizes can be well approximated by a power-law (with exponent, eta = -3.4 ± 0.2), which is very similar to that found for Galactic giant molecular clouds and young massive star clusters in merging galaxies, suggesting a common fractal nature imposed by turbulent gas. The size distribution is also remarkably similar to that of Galactic globular clusters, indicating that cluster disruption is largely independent of cluster radius. We do not find any strong trends between the age and mass, mass and effective radius, nor between the galactocentric distance and effective radius. There is, however, a strong correlation between the age of a cluster and its extinction, with younger clusters being more heavily reddened than older clusters. Ref III: Gieles, M.; Bastian, N.; Lamers, H. J. G. L. M.; Mout, J. N. [astro-ph/0506066 ] A&A 441 (2005) 949

K8 Gas Clouds Yield Important Clues Supporting Theory on Spiral Arms

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	Authors: Schinnerer, Eva; Weiss, Axel; Scoville, Nicholas Z.; Aalto, Susanne
	Journal-ref: IAUS 221 (2003) 145 [ ]
	Title: Molecular Gas and Star Formation in the Spiral Arms of M51
Abstract: The Whirlpool galaxy M51 one of the closest almost face-on grand-design spiral galaxies has about 50% of its molecular gas in the spectacular grand-design spiral arms. Besides the large number of Giant Molecular Cloud Associations (GMAs) (up to 16 within one spiral arm) numerous OB star clusters reside in the spiral arms as is obvious in high resolution HST data. We mapped six key molecular line probes at high angular resolution (~ 2"") in two distinct regions of the spiral arms using the OVRO mm-interferometer. The line data are used to determine the physical properties of the molecular gas such as density and temperature. Comparison between different sites of active star formation reveals correlations between the molecular gas properties and on-going massive star formation. The high angular and spectral resolution permits us to investigate the kinematics between the GMAs (as well as within the GMAs) and the effects of shear and streaming motion on the stability of the GMAs. [astro-ph/0702310 ]

Astronomers studying gas clouds in the famous Whirlpool Galaxy have found important clues supporting a theory that seeks to explain how the spectacular spiral arms of galaxies can persist for billions of years. The astronomers applied techniques used to study similar gas clouds in our own Milky Way to those in the spiral arms of a neighbor galaxy for the first time, and their results bolster a theory first proposed in 1964.

The spiral galaxy M51:
Left, as seen with the Hubble Space Telescope;
Right, radio image showing location of Carbon Monoxide gas.
CREDIT: STScI, OVRO, IRAM

The Whirlpool Galaxy, about 31 million light-years distant, is a beautiful spiral in the constellation Canes Venatici. Also known as M51, it is seen nearly face-on from Earth and is familiar to amateur astronomers and has been featured in countless posters, books and magazine articles.

"This galaxy made a great target for our study of spiral arms and how star formation works along them," said Eva Schinnerer, of the National Radio Astronomy Observatory in Socorro, NM. "It was ideal for us because it's one of the closest face-on spirals in the sky," she added.

Schinnerer worked with Axel Weiss of the Institute for Millimeter Radio Astronomy (IRAM) in Spain, Susanne Aalto of the Onsala Space Observatory in Sweden, and Nick Scoville of Caltech. The astronomers presented their findings to the American Astronomical Society's meeting in Denver, Colorado.

The scientists analyzed radio emission from Carbon Monoxide (CO) molecules in giant gas clouds along M51's spiral arms. Using telescopes at Caltech's Owens Valley Radio Observatory and the 30-meter radio telescope of IRAM, they were able to determine the temperatures and amounts of turbulence within the clouds. Their results provide strong support for a theory that "density waves" explain how spiral arms can persist in a galaxy without winding themselves so tightly that, in effect, they disappear.

ESO / ISOCAM
ISOCAM map of the Whirlpool Galaxy (M51)
The density-wave theory, proposed by Frank Shu and C.C. Lin in 1964, says that a galaxy's spiral pattern is a wave of higher density, or compression, that revolves around the galaxy at a speed different from that of the galaxy's gas and stars. Schinnerer and her colleagues studied a region in one of M51's spiral arms that presumably has just overtaken and passed through the density wave.

Their data indicate that gas on the trailing edge of the spiral arm, which has most recently passed through the density wave, is both warmer and more turbulent than gas in the forward edge of the arm, which would have passed through the density wave longer ago.

"This is what we would expect from the density-wave theory," Schinnerer said. "The gas that passed through the density wave earlier has had time to cool and lose the turbulence caused by the passage," she added.

"Our results show, for the first time, how the density wave operates on a cloud-cloud scale, and how it promotes and prevents star formation in spiral arms," Aalto said.

The next step, the scientists say, is to look at other spiral galaxies to see if a similar pattern is present. That will have to wait, Schinnerer said, because the radio emission from CO molecules that provides the information on temperature and turbulence is very faint.

"When the Atacama Large Millimeter Array (ALMA) comes on line, it will have the ability to extend this type of study to other galaxies. We look forward to using ALMA to test the density-wave model more thoroughly," Schinnerer said. ALMA is a millimeter-wave observatory that will use 64, 12-meter-diameter dish antennas on the Atacama Desert of northern Chile. Now under construction, ALMA will provide astronomers with an unprecedented capability to study the Universe at millimeter wavelengths.

K9 Out of This Whirl: the Whirlpool Galaxy (M51) and Companion Galaxy

Hubble's 15th Anniversary:
Images of M51 (the Whirlpool Galaxy) and M16 (the Eagle Nebula). To celebrate its birthday, the team at the Space Telescope Science Institute (STScI) in Baltimore, Maryland, Hubble's operational home, unveiled two magnificent new images of classic astronomy scenes: the Whirlpool Galaxy (Messier 51) in Canes Venatici and a column of gas in the Eagle Nebula (Messier 16) in Serpens, home to Hubble's earlier, epic image, the "Pillars of Creation."
M51:
This image, which has been greatly reduced in resolution here, only hints at the amazing detail in the new Hubble Space Telescope Advanced Camera for Surveys' view of the Whirlpool Galaxy (Messier 51).
Courtesy NASA, ESA, S. Beckwith (STScI), and The Hubble Heritage Team (STScI/AURA).

NASA released new views today [25-04-2005] of two of the most well-known objects Hubble has ever observed: the Whirlpool Galaxy (spiral galaxy M51) [left] and the Eagle Nebula [right].

These new images are among the largest and sharpest Hubble has ever taken. They were made with Hubble's newest camera, the Advanced Camera for Surveys (ACS). The images are so incredibly sharp, they could be enlarged to billboard size and still retain stunning details.

For the 15th anniversary, scientists used the ACS to record a new region of the eerie-looking Eagle Nebula. The Eagle Nebula image reveals a tall, dense tower of gas being sculpted by ultraviolet light from a group of massive, hot stars.

The new Whirlpool Galaxy image showcases the spiral galaxy's classic features, from its curving arms, where newborn stars reside, to its yellowish central core that serves as home for older stars. A feature of considerable interest is the companion galaxy located at the end of one of the spiral arms.

The graceful, winding arms of the majestic spiral galaxy M51 (NGC 5194) appear like a grand spiral staircase sweeping through space. They are actually long lanes of stars and gas laced with dust.

This sharpest-ever image of the Whirlpool Galaxy, taken in January 2005 with the Advanced Camera for Surveys aboard NASA's Hubble Space Telescope, illustrates a spiral galaxy's grand design, from its curving spiral arms, where young stars reside, to its yellowish central core, a home of older stars. The galaxy is nicknamed the Whirlpool because of its swirling structure.

The Whirlpool's most striking feature is its two curving arms, a hallmark of so-called grand-design spiral galaxies. Many spiral galaxies possess numerous, loosely shaped arms which make their spiral structure less pronounced. These arms serve an important purpose in spiral galaxies. They are star-formation factories, compressing hydrogen gas and creating clusters of new stars. In the Whirlpool, the assembly line begins with the dark clouds of gas on the inner edge, then moves to bright pink star-forming regions, and ends with the brilliant blue star clusters along the outer edge.

Composite optical - ISOCAM image of M51
Some astronomers believe that the Whirlpool's arms are so prominent because of the effects of a close encounter with NGC 5195, the small, yellowish galaxy at the outermost tip of one of the Whirlpool's arms. At first glance, the compact galaxy appears to be tugging on the arm. Hubble's clear view, however, shows that NGC 5195 is passing behind the Whirlpool. The small galaxy has been gliding past the Whirlpool for hundreds of millions of years.

As NGC 5195 drifts by, its gravitational muscle pumps up waves within the Whirlpool's pancake-shaped disk. The waves are like ripples in a pond generated when a rock is thrown in the water. When the waves pass through orbiting gas clouds within the disk, they squeeze the gaseous material along each arm's inner edge. The dark dusty material looks like gathering storm clouds. These dense clouds collapse, creating a wake of star birth, as seen in the bright pink star-forming regions. The largest stars eventually sweep away the dusty cocoons with a torrent of radiation, hurricane-like stellar winds, and shock waves from supernova blasts. Bright blue star clusters emerge from the mayhem, illuminating the Whirlpool's arms like city streetlights.

The Whirlpool is one of astronomy's galactic darlings. Located 31 million light-years away in the constellation Canes Venatici (the Hunting Dogs), the Whirlpool's beautiful face-on view and closeness to Earth allow astronomers to study a classic spiral galaxy's structure and star-forming processes.

Literatur zu "M51"
Ji-Feng Liu, Joel N. Bregman, Jimmy Irwin, Patrick Seitzer	2002	ApJ 581, L93-6	"An Ultra-luminous X-Ray Object with a 2 hour period in M51"
G.C. Dewangan, R.E. Griffiths, M. Choudhury, T. Miyaji, N.J. Schurch	2005	ApJ 635, 198-213	"XMM-Newton view of the ultra-luminous X-ray sources in M51"
W. L. Freedman	2002	IJMP A17S1, 58-69	"The Measure of Cosmological Parameters"
L. E. Kuchinski, B. F. Madore, W. L. Freedman & M. Trewella	2001	AJ 122, 729	"Quantitative Morphology of Galaxies Observed in the Ultraviolet"
D. Calzetti, R.C. Kennicutt, L. Bianchi, et al.	2005	ApJ 633, 871-93	"Star Formation in NGC5194 (M51a): The Panchromatic View from GALEX to Spitzer"
N. Bastian, M. Gieles, et al.	2004	A&A 431, 905/td>	"The Star Cluster Population of M51: II. Age distribution and ..."

H. Heintzmann

( Eintrag vom 5.3.2006)

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