648 research outputs found
Galaxy Evolution in Local Group Analogs. I. A GALEX study of nearby groups
Understanding the astrophysical processes acting within galaxy groups and
their effects on the evolution of the galaxy population is one of the crucial
topic of modern cosmology, as almost 60% of galaxies in the Local Universe are
found in groups. We imaged in the far (FUV 1539 A) and near ultraviolet (NUV
2316 A) with GALEX three nearby groups, namely LGG93, LGG127 and LGG225. We
obtained the UV galaxy surface photometry and, for LGG225, the only group
covered by the SDSS, the photometry in u, g, r, i, z bands. We discuss galaxy
morphologies looking for interaction signatures and we analyze the SED of
galaxies to infer their luminosity-weighted ages. The UV and optical photometry
was also used to perform a kinematical and dynamical analysis of each group and
to evaluate the stellar mass. A few member galaxies in LGG225 show a distorted
UV morphology due to ongoing interactions. (FUV-NUV) colors suggest that
spirals in LGG93 and LGG225 host stellar populations in their outskirts younger
than that of M31 and M33 in the LG or with less extinction. The irregular
interacting galaxy NGC3447A has a significantly younger stellar population (few
Myr old) than the average of the other irregular galaxies in LGG225 suggesting
that the encounter triggered star formation. The early-type members of LGG225,
NGC3457 and NGC3522, have masses of the order of a few 10^9 Mo, comparable to
the Local Group ellipticals. For the most massive spiral in LGG225, we estimate
a stellar mass of ~4x10 Mo, comparable to M33 in the LG. Ages of stellar
populations range from a few to ~7 Gyr for the galaxies in LGG225. The
kinematical and dynamical analysis indicates that LGG127 and LGG225 are in a
pre-virial collapse phase, i.e. still undergoing dynamical relaxation, while
LGG93 is likely virialized. (Abridged)Comment: 20 pages, 13 figures, accepted for publication in Astronomy and
Astrophysic
Dissecting Kinematics and Stellar Populations of Counter-Rotating Galaxies with 2-Dimensional Spectroscopy
We present a spectral decomposition technique and its applications to a
sample of galaxies hosting large-scale counter-rotating stellar disks. Our
spectral decomposition technique allows to separate and measure the kinematics
and the properties of the stellar populations of both the two counter-rotating
disks in the observed galaxies at the same time. Our results provide new
insights on the epoch and mechanism of formation of these galaxies.Comment: 4 pages, 3 figures. Contributed talk presented at the Conference
"Multi-Spin galaxies", September 30 - October 3, 2013, INAF-Astronomical
Observatory of Capodimonte, Naples, Italy. To be published in ASP Conf. Ser.,
Multi-Spin Galaxies, ed. E. Iodice & E. M. Corsini (San Francisco: ASP
The mid-UV population of the nucleus and the bulk of the post-merger NGC 3610
The very center of NGC~3610, a clearly disturbed giant elliptical generally
assumed to be a post-merger remnant, appears dominated in the mid-UV (2500-3200
A spectral region) by a stellar population markedly different from that
dominating the bulk of its stellar body. I want here to make use of the mid-UV
spectra of NGC~3610 as seen through tiny (1") and large (10"20")
apertures as a diagnostic population tool. I compare archive IUE/LWP large
aperture and HST/FOS UV data of NGC 3610. The strength of mid-UV triplet
(dominated by the turnoff population) shows a remarkable drop when switching
from the galaxy central arcsec (FOS aperture) to an aperture size comparable to
0.5 r (IUE). The sub-arsec (mid)-UV properties of this galaxy
involved in a past merger reveal a central metal enrichment which left intact
the bulk of its pre-existing population.Comment: 6 pages, 2 figures, accepted for publication in astronomy and
Astrophysic
Bimodality in low-luminosity E and S0 galaxies
Stellar population characteristics are presented for a sample of low-luminosity early-type galaxies (LLEs) in order to compare them with their more luminous counterparts. Long-slit spectra of a sample of 10 LLEs were taken with the ESO New Technology Telescope, selected for their low luminosities. Line strengths were measured on the Lick standard system. Lick indices for these LLEs were correlated with velocity dispersion (σ), alongside published data for a variety of Hubble types. The LLEs were found to fall below an extrapolation of the correlation for luminous ellipticals and were consistent with the locations of spiral bulges in plots of line strengths versus σ. Luminosity weighted average ages, metallicities and abundance ratios were estimated from χ2 fitting of 19 Lick indices to predictions from simple stellar population models. The LLEs appear younger than luminous ellipticals and of comparable ages to spiral bulges. These LLEs show a bimodal metallicity distribution, consisting of a low-metallicity group (possibly misclassified dwarf spheroidal galaxies) and a high-metallicity group (similar to spiral bulges). Finally, they have low α-element to iron peak abundance ratios indicative of slow, extended star formation
Early Type Galaxies in the Mid Infrared: a new flavor to their stellar populations
The mid infrared emission of early type galaxies traces the presence of
intermediate age stellar populations as well as even tiny amounts of ongoing
star formation. Here we discuss high S/N Spitzer IRS spectra of a sample of
Virgo early type galaxies, with particular reference to NGC 4435. We show that,
by combining mid infrared spectroscopic observations with existing broad band
fluxes, it is possible to obtain a very clean picture of the nuclear activity
in this galaxy.Comment: 4 pages; proceedings of IAU Symposium No. 241, "Stellar Populations
as Building Blocks of Galaxies", editors A. Vazdekis and R. Peletie
Is the Giant Elliptical Galaxy NGC5018 a Post-Merger Remnant?
NGC5018, one of the weakest UV emitters among giant ellipticals (gE) observed
with IUE, appears to consist of an optical stellar population very similar to
that of the compact, dwarf elliptical M32, which is several magnitudes fainter
in luminosity than NGC5018 and whose stellar population is know to be ~3 Gyr
old. Here we show that the mid-UV spectra of these two galaxies are also very
similar down to an angular scale hundreds times smaller than the IUE large
aperture (as probed by HST/FOS UV spectra obtained through 0.86 arcsec
apertures). This implies a reasonably close match of the populations dominating
their mid-UV light (namely, their main-sequence turnoff stars). These data
indicate that NGC5018 has, in its inner regions, a rather uniform dominance of
a ~3 Gyr-old stellar population, probably a bit different in metallicity from
M32. Combined with the various structures that indicate that NGC5018 is the
result of a recent major merger, it appears that almost all of stars we see in
its center regions were formed about 3 Gyr ago, in that merger event. NGC5018
is likely the older brother of NGC7252, the canonical gE-in-formation merger.
As such, NGC5018 is perhaps the best galaxy which can tell us how a merger
works, after the fireworks subside, to form a gE galaxy today. For this reason
alone, the stellar populations in NGC5018 at all radii are worth studying in
detail.Comment: 4 pages, 3 figures, LaTeX. Accepted for publication in Astronomy &
Astrophysic
Objects in NGC 205 Resolved into Stellar Associations by HST Ultraviolet Imaging
We have obtained high resolution UV images with the HST+WFPC2 of the central region of the dwarf elliptical galaxy NGC 205. Our images reveal that many of the hot UV stars previously detected and studied from the ground are actually multiple systems, open clusters and star associations. We have performed photometry of two such clusters and we find our data are consistent with stellar ages of 50 and 100 Myr, respectively. From the number of massive stars in NGC 205 we estimate that the star formation episode in this galaxy has turned ~1,000 Msolar of gas into stars over the last 100 Myr
Kinematic and stellar population properties of the counter-rotating components in the S0 galaxy NGC 1366
Context. Many disk galaxies host two extended stellar components that rotate in opposite directions. The analysis of the stellar populations of the counter-rotating components provides constraints on the environmental and internal processes that drive their formation. Aims. The S0 NGC 1366 in the Fornax cluster is known to host a stellar component that is kinematically decoupled from the main body of the galaxy. Here we successfully separated the two counter-rotating stellar components to independently measure the kinematics and properties of their stellar populations. Methods. We performed a spectroscopic decomposition of the spectrum obtained along the galaxy major axis and separated the relative contribution of the two counter-rotating stellar components and of the ionized-gas component. We measured the line-strength indices of the two counter-rotating stellar components and modeled each of them with single stellar population models that account for the \u3b1/Fe overabundance. Results. We found that the counter-rotating stellar component is younger, has nearly the same metallicity, and is less \u3b1/Fe enhanced than the corotating component. Unlike most of the counter-rotating galaxies, the ionized gas detected in NGC 1366 is neither associated with the counter-rotating stellar component nor with the main galaxy body. On the contrary, it has a disordered distribution and a disturbed kinematics with multiple velocity components observed along the minor axis of the galaxy. Conclusions. The different properties of the counter-rotating stellar components and the kinematic peculiarities of the ionized gas suggest that NGC 1366 is at an intermediate stage of the acquisition process, building the counter-rotating components with some gas clouds still falling onto the galaxy. \ua9 ESO 2017
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