scholarly journals Stellar Associations in the Tail of NGC 4038

2004 ◽  
Vol 217 ◽  
pp. 546-549 ◽  
Author(s):  
I. Saviane ◽  
J. E. Hibbard ◽  
R. M. Rich
Keyword(s):  
Stellar Population ◽  
Dwarf Galaxy ◽  
Hubble Space Telescope ◽  
Neutral Hydrogen ◽  
Distance Modulus ◽  
Wide Field ◽  
Tidal Tail ◽  
Central Regions ◽  
Red Giant ◽  
Super Star Clusters

We have used the Hubble Space Telescope and Wide Field Planetary Camera 2 to image the putative tidal dwarf galaxy located at the tip of the Southern tidal tail of NGC 4038/9, the Antennae. We resolve individual stars, and identify two stellar populations. Hundreds of massive stars are present, concentrated into tight OB associations on scales of 200 pc, with ages ranging from 2-100 Myr. An older stellar population is distributed roughly following the outer contours of the neutral hydrogen in the tidal tail; we associate these stars with material ejected from the outer disks of the two spirals. The older stellar population has a red giant branch tip at I = 26.5 ± 0.2 from which we derive a distance modulus (m - M)0 = 30.7 ± 0.25. The implied distance of 13.8 ± 1.7 Mpc is nearly a factor of two closer than commonly quoted distances for NGC 4038/9. In contrast to the previously studied core of the merger, we find no super star clusters. One might conclude that SSCs require the higher pressures found in the central regions in order to form, while spontaneous star formation in the tail produces the kind of O-B star associations seen in dwarf irregular galaxies.

scholarly journals The Nearby Young Dwarf Galaxy SBS 0335-052: Primordial Gas and Lyman-Alpha Emission

1998 ◽  
Vol 11 (1) ◽  
pp. 115-116
Author(s):  
Trinh Xuan Thuan ◽  
Yuri I. Izotov
Keyword(s):  
Star Formation ◽  
Stellar Population ◽  
Dwarf Galaxy ◽  
Neutral Hydrogen ◽  
Hydrogen Gas ◽  
Gas Content ◽  
Ionized Gas ◽  
Filamentary Structure ◽  
A Chain ◽  
Super Star Clusters

Ever since their discovery, blue compact dwarf (BCD) galaxies have been thought of as excellent candidates for being young galaxies, i.e. systems presently undergoing one of their very first bursts of star formation. This is mainly because BCDs are very metal-deficient, the metallicities of their ionized gas ranging between Zʘ/50 and Zʘ/3, which makes them the least chemically evolved galaxies in the Universe. Other evidence, such as the very high fractional neutral hydrogen gas content and the lack of an evident underlying old stellar population on optical images, also point to the relative youth of some BCDs. Thuan, Izotov h Lipovetsky (1997) have argued SBS 0335-052 to be a young galaxy on the basis of the following evidence: 1) HST imaging of the BCD shows its underlying extended low surface brightness component to have an irregular and filamentary structure, suggesting that a significant part of the emission (~1/3) comes not from an underlying stellar population, but from ionized gas. Any underlying stellar population must be younger than ~108yr. Propagating star formation occurs in a chain of 6 super-star clusters with ages ranging between 4 and 30 Myr. 2) The underlying component shows unusually blue colors consistent with gaseous emission, in contrast to most BCDs which possess an underlying red component. 3) VLA 21 cm observations show the BCD to be embedded in an extraordinarily large HI cloud with dimensions some 64 × 24 kpc (the typical size of HI envelopes around BCDs is more like a few kpc in each dimension).

scholarly journals Young Stars in the Outer Disc of NGC 6822

2004 ◽  
Vol 217 ◽  
pp. 168-169
Author(s):  
W. J. G de Blok ◽  
F. Walter
Keyword(s):  
Interstellar Medium ◽  
Stellar Population ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Neutral Hydrogen ◽  
Young Stars ◽  
Wide Field ◽  
Chemical Enrichment ◽  
Ngc 6822

We present wide-field optical imaging covering the entire neutral hydrogen disc of the Local Group dwarf galaxy NGC 6822. These observations reveal the presence of numerous young stars at large galactocentric radii. The extended distribution of young stars implies that stars do form in the outer disks of dwarf galaxies; the HI is not necessarily much more extended than the stellar population. This finding has important consequences for the chemical enrichment of the interstellar medium throughout dwarf galaxies.

scholarly journals How Massive is the Black Hole in M87?

1995 ◽  
Vol 10 ◽  
pp. 535-538
Author(s):  
S.K. Chakrabarti
Keyword(s):  
Black Hole ◽  
Dwarf Galaxy ◽  
Hubble Space Telescope ◽  
Elliptical Galaxy ◽  
Wide Field ◽  
Line Profiles ◽  
Present Contribution ◽  
Doppler Shifts ◽  
Spiral Structures ◽  
Armed Spiral

Using the Faint Object Spectrograph (FOS) on Hubble Space Telescope (HST), Harms et al. (1994, H94) have recently reported the spectroscopy of central region of the elliptical galaxy M87. Ford et al. 1994 (hereafter F94), using Wide Field Planetary Camera-2 have imaged the region around the nucleus in Hα+[NII] and find an ionized disk with spiral structures of mainly two arms. From the kinematical argument, based on the Doppler shifts of several lines emitted from the disk, and assuming a Keplerian motion of the emitting gas, they conclude that the mass of the disk plus the nucleus: Mc(R < 18pc) = (2.4± 0.7)× 109M⊙ and the inclination angle of the disk with the line of sight is i = (42±5)°. However, if the bright spiral structures are real, and represent shocked region in the disk, we expect that the disk is strongly non-Keplerian and therefore the mass of the black hole must be higher than above estimation.In the present contribution, we provide a complete description of the velocity field of the ionized disk and compute the shape of typical line profiles expected from various parts of the disk. Our analysis is based on the solution of a non-axisymmetric disk which includes two armed spiral density waves. We find a very good agreement between the theoretical and observed line profiles as regards to the Doppler shifts, line widths and the intensity ratios and estimate the mass of the black hole to be (4 ± 0.2) × 109M⊙. Details of this work will be published elsewhere (Chakrabarti, 1995).In a binary system with a thin accretion disk, the binary companion can induce two armed spiral shocks in the disk (e.g., Matsuda et al. 1987, Spruit 1987, Chakrabarti & Matsuda, 1992). In the case of active galaxies, a passing companion (or a globular cluster or a dwarf galaxy) which is more massive than the disk can induce the same effect.

scholarly journals The multipopulation phenomenon in Galactic globular clusters: M4 and M22

2009 ◽  
Vol 5 (S266) ◽  
pp. 326-332
Author(s):  
S. Villanova ◽  
G. Piotto ◽  
A. F. Marino ◽  
A. P. Milone ◽  
A. Bellini ◽  
...  
Keyword(s):  
High Resolution ◽  
Spectroscopic Data ◽  
Globular Clusters ◽  
Stellar Population ◽  
The Other ◽  
Wide Field ◽  
Galactic Globular Clusters ◽  
Red Giant ◽  
Process Elements ◽  
Different Characteristics

AbstractWe present an abundance analysis based on high-resolution spectra of red-giant-branch (RGB) stars in the Galactic globular clusters NGC 6121 (M4) and NGC 6656 (M22). Our aim was to study their stellar population in the context of the multipopulation phenomenon recently discovered to affect some globular clusters. Analysis was performed for the following elements: O, Na, Mg, Al, Ca, Fe, Y, and Ba. Spectroscopic data were completed by high-precision wide-field U BV IC ground-based photometry and HST/ACS observations. For M4, we find a well-defined Na–O anticorrelation composed of two distinct groups of stars with significantly different Na and O content. The two groups of Na-rich and Na-poor stars populate two different regions along the RGB. As regards M22, Na and O follow the well-known anticorrelation found in many other GCs. However, at odds with M4, it appears to be continuous without any hint of clumpiness. On the other hand, we identified two clearly separated groups of stars with significantly different abundances of the s-process elements Y, Zr and Ba. The relative numbers of the members of both groups are very similar to the ratio of the stars in the two subgiant branches of M22 recently found by Piotto (2009). The s-element-rich stars are also richer in iron and have higher Ca abundances. This makes M22 the second cluster after ω Centauri where an intrinsic spread in Fe was found. Both spectroscopic and photometric results imply the presence of two stellar populations in M4 and M22, even if both clusters have completely different characteristics.

scholarly journals Stellar Populations and Local Group Membership of the Dwarf Galaxy DDO 210

1999 ◽  
Vol 192 ◽  
pp. 268-271
Author(s):  
Myung Gyoon Lee
Keyword(s):  
Stellar Population ◽  
Local Group ◽  
Group Membership ◽  
Dwarf Galaxy ◽  
Stellar Populations ◽  
Young Stars ◽  
Ccd Photometry ◽  
A Value ◽  
Red Giant

Deep BVI CCD photometry of dwarf galaxy DD0 210 obtained in this study shows that the resolved stellar population in this galaxy consists of a dominant old red giant population and some young stars. We have estimated the distance to this galaxy using the I-band magnitude of the tip of the red giant branch, obtaining a value of 1030±50 kpc. This result combined with the velocity of DDO 210 shows that DDO 210 is a member of the Local Group.

scholarly journals Hubble Space Telescope photometry of multiple stellar populations in the inner parts of NGC 2419

2019 ◽  
Vol 624 ◽  
pp. A25 ◽  
Author(s):  
Søren S. Larsen ◽  
Holger Baumgardt ◽  
Nate Bastian ◽  
Svea Hernandez ◽  
Jean Brodie
Keyword(s):  
Hubble Space Telescope ◽  
Dynamical Evolution ◽  
Bimodal Distribution ◽  
Wide Field ◽  
Red Giants ◽  
Space Telescope ◽  
Deep Imaging ◽  
Central Regions ◽  
Average Rotation ◽  
The Difference

We present new deep imaging of the central regions of the remote globular cluster NGC 2419, obtained with the F343N and F336W filters of the Wide Field Camera 3 on board the Hubble Space Telescope. The new data are combined with archival imaging to constrain nitrogen and helium abundance variations within the cluster. We find a clearly bimodal distribution of the nitrogen-sensitive F336W–F343N colours of red giants, from which we estimate that about 55% of the giants belong to a population with about normal (field-like) nitrogen abundances (P1), while the remaining 45% belong to a nitrogen-rich population (P2). On average, the P2 stars are more He-rich than the P1 stars, with an estimated mean difference of ΔY ≃ 0.05, but the P2 stars exhibit a significant spread in He content and some may reach ΔY ≃ 0.13. A smaller He spread may also be present for the P1 stars. Additionally, stars with spectroscopically determined low Mg abundances ([Mg/Fe] <  0) are generally associated with P2. We find the P2 stars to be slightly more centrally concentrated in NGC 2419 with a projected half-number radius of about 10% less than for the P1 stars, but the difference is not highly significant (p ≃ 0.05). Using published radial velocities, we find evidence of rotation for the P1 stars, whereas the results are inconclusive for the P2 stars, which are consistent with no rotation as well as the same average rotation found for the P1 stars. Because of the long relaxation time scale of NGC 2419, the radial trends and kinematic properties of the populations are expected to be relatively unaffected by dynamical evolution. Hence, they provide constraints on formation scenarios for multiple populations, which must account not only for the presence of He spreads within sub-populations identified via CNO variations, but also for the relatively modest differences in the spatial distributions and kinematics of the populations.

scholarly journals A CFH12K Survey of Red Giant Stars in the M81 Group

2004 ◽  
Vol 217 ◽  
pp. 90-91 ◽  
Author(s):  
Patrick R. Durrell ◽  
Megan E. DeCesar ◽  
Robin Ciardullo ◽  
Denise Hurley-Keller ◽  
John J. Feldmeier
Keyword(s):  
Asymptotic Giant Branch ◽  
Wide Field ◽  
Agb Stars ◽  
Field Sampling ◽  
Giant Stars ◽  
Tidal Tail ◽  
Dimensional Distribution ◽  
Red Giant ◽  
The Many ◽  
Tidal Tails

We present the preliminary results of a wide-field photometric survey of individual red giant branch (RGB) and asymptotic giant branch (AGB) stars in the M81 group, performed with the CFH12K mosaic camera of the CFHT. We use deep VI images of 0.65 sq. deg. of sky to map out the two-dimensional distribution of intragroup stars and to search for stars associated with the many HI tidal tails in the group. We place an upper limit on the presence of metal-poor RGB stars in a field located 50-80 kpc from M81, and derive an ‘intragroup’ fraction of < 2%. In a field sampling the M81-NGC3077 HI tidal tail, we find blue stars associated with some of the tidal features, including 2 clumps which we tentatively describe as tidal dwarf candidates. These objects are ~ 1 kpc in size, and, based on their color-magnitude diagrams, have formed stars as recently as ~ 30 – 70 Myr ago, long after the group's most recent interactions.

scholarly journals Is Fornax 4 the nuclear star cluster of the Fornax dwarf spheroidal galaxy?

2020 ◽  
Vol 495 (4) ◽  
pp. 4518-4528
Author(s):  
S Martocchia ◽  
E Dalessandro ◽  
M Salaris ◽  
S Larsen ◽  
M Rejkuba
Keyword(s):  
Stellar Population ◽  
Hubble Space Telescope ◽  
Detailed Comparison ◽  
Observational Evidence ◽  
Star Cluster ◽  
The Other ◽  
Horizontal Branch ◽  
The Galaxy ◽  
Red Giant

ABSTRACT Fornax 4 is the most distinctive globular cluster in the Fornax dwarf spheroidal. Located close to the centre of the galaxy, more metal-rich and potentially younger than its four companions (namely, Fornax clusters number 1, 2, 3, and 5), it has been suggested to have experienced a different formation than the other clusters in the galaxy. Here, we use Hubble Space Telescope/WFC3 photometry to characterize the stellar population content of this system and shed new light on its nature. By means of a detailed comparison of synthetic horizontal branch and red giant branch with the observed colour–magnitude diagrams, we find that this system likely hosts stellar sub-populations characterized by a significant iron spread up to Δ[Fe/H] ∼ 0.4 dex and possibly by also some degree of He abundance variations ΔY ∼ 0.03. We argue that this purely observational evidence, combined with the other peculiarities characterizing this system, supports the possibility that Fornax 4 is the nuclear star cluster of the Fornax dwarf spheroidal galaxy. A spectroscopic follow-up for a large number of resolved member stars is needed to confirm this interesting result and to study in detail the formation and early evolution of this system and more in general the process of galaxy nucleation.

scholarly journals The Distance and Dynamical History of the Virgo Cluster Ultradiffuse Galaxy VCC 615

2022 ◽  
Vol 924 (2) ◽  
pp. 87
Author(s):  
J. Christopher Mihos ◽  
Patrick R. Durrell ◽  
Elisa Toloba ◽  
Patrick Côté ◽  
Laura Ferrarese ◽  
...  
Keyword(s):  
Dwarf Galaxy ◽  
Hubble Space Telescope ◽  
Virgo Cluster ◽  
Cluster Center ◽  
Main Body ◽  
The Galaxy ◽  
Orbit Modeling ◽  
History Of ◽  
Red Giant ◽  
Distance Estimator

Abstract We use deep Hubble Space Telescope imaging to derive a distance to the Virgo Cluster ultradiffuse galaxy (UDG) VCC 615 using the tip of the red giant branch (TRGB) distance estimator. We detect 5023 stars within the galaxy, down to a 50% completeness limit of F814W ≈ 28.0, using counts in the surrounding field to correct for contamination due to background sources and Virgo intracluster stars. We derive an extinction-corrected F814W tip magnitude of m tip , 0 = 27.19 − 0.05 + 0.07 , yielding a distance of d = 17.7 − 0.4 + 0.6 Mpc. This places VCC 615 on the far side of the Virgo Cluster (d Virgo = 16.5 Mpc), at a Virgocentric distance of 1.3 Mpc and near the virial radius of the main body of Virgo. Coupling this distance with the galaxy’s observed radial velocity, we find that VCC 615 is on an outbound trajectory, having survived a recent passage through the inner parts of the cluster. Indeed, our orbit modeling gives a 50% chance the galaxy passed inside the Virgo core (r < 620 kpc) within the past gigayear, although very close passages directly through the cluster center (r < 200 kpc) are unlikely. Given VCC 615's undisturbed morphology, we argue that the galaxy has experienced no recent and sudden transformation into a UDG due to the cluster potential, but rather is a long-lived UDG whose relatively wide orbit and large dynamical mass protect it from stripping and destruction by the Virgo cluster tides. Finally, we also describe the serendipitous discovery of a nearby Virgo dwarf galaxy projected 90″ (7.2 kpc) away from VCC 615.

scholarly journals The distance to M31 in the era of precision cosmology

2012 ◽  
Vol 8 (S289) ◽  
pp. 235-235
Author(s):  
David Valls-Gabaud
Keyword(s):  
Large Scale ◽  
Near Infrared ◽  
Hubble Space Telescope ◽  
Three Dimensional ◽  
Eclipsing Binaries ◽  
Wide Field ◽  
Acoustic Oscillations ◽  
Data Set ◽  
Red Giant ◽  
Precision Cosmology

AbstractWith the advent of precision cosmology, where distances out to redshifts z < 0.6 can be measured to 2% precision on the basis of baryon acoustic oscillations, it appears essential to establish an accurate calibration of the primary and secondary indicators of the cosmological distance ladder. Here we review recent attempts at anchoring M31 very accurately using three independent methods, and discuss in detail the systematics that affect each. Two double-lined eclipsing binaries yield a distance to M31 which is precise to 4%. New Bayesian methods have been applied to determine the tip of the red-giant branch, even in sparsely populated colour–magnitude diagrams, and provide unique insights in the context of a precise three-dimensional distribution of the satellites in the M31 system. Over 2500 Cepheids have been identified in large-scale multi-colour surveys of M31, the largest homogeneous data set thus far obtained for any galaxy. A subset of 68 with periods longer than 10 days have been observed with the Wide-Field Camera 3 on board the Hubble Space Telescope, yielding the tightest-ever near-infrared period–luminosity relation, with a mean distance error of 1%. Combined with other measurements, the distance to M31 is now measured with a precision of 3%. Forthcoming improvements, and their implications, are also discussed.

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