23 research outputs found
Modelling and interpreting optical spectra of galaxies at R=10000
One way to extract more information from the integrated light of galaxies is
to improve the spectral resolution at which observations and analysis are
carried out. The population synthesis code currently providing the highest
spectral resolution is Pegase-HR, which was made available by D. Le Borgne et
al. in 2004. Based on an empirical stellar library, it provides synthetic
spectra between 4000 and 6800 A at lambda/d(lambda)=10000 for any star
formation history, with or without chemical evolution. Such a resolution is
particularly useful for the study of low mass galaxies, massive star clusters,
or other galaxy regions with low internal velocity dispersions.
After a summary of the main features of Pegase-HR and comparisons with other
population synthesis codes, this paper focuses on the inversion of optical
galaxy spectra. We explore the limits of what information can or can not be
recovered, based on theoretical principles and extensive simulations. First
applications to extragalactic objects are shown.Comment: Inv. talk in "The Spectral Energy Distribution of Gas-Rich Galaxies:
Confronting Models with Data", Heidelberg, 4-8 Oct. 2004, eds. C.C. Popescu
and R.J. Tuffs, AIP Conf. Ser., in pres
The Next Generation Virgo cluster Survey. V. modelling the dynamics of M87 with the Made-to-Measure method
We study the dynamics of the giant elliptical galaxy M87 from the central to
the outermost regions with the made-to-measure (M2M) method. We use a new
catalogue of 922 globular cluster line-of- sight velocities extending to a
projected radius of 180 kpc (equivalent to 25 M87 effective radii), and SAURON
integral field unit data within the central 2.4 kpc. 263 globular clusters,
mainly located beyond 40 kpc, are newly observed by the Next Generation Virgo
Survey (NGVS). For the M2M modelling, the gravitational potential is taken as a
combination of a luminous matter potential with a constant stellar
mass-to-light ratio and a dark matter potential modelled as a logarithmic
potential. Our best dynamical model returns a stellar mass-to-light ratio in
the I band of M/LI = 6.0(+ -0.3) M_sun/L_sun with a dark matter potential scale
velocity of 591(+ -50) km/s and scale radius of 42(+ -10) kpc. We determine the
total mass of M87 within 180 kpc to be (1.5 + - 0.2) 10^13 M_sun. The mass
within 40 kpc is smaller than previous estimates determined using globular
cluster kinematics that did not extend beyond 45 kpc. With our new globular
cluster velocities at much larger radii, we see that globular clusters around
40 kpc show an anomalously large velocity dispersion which affected previous
results. The mass we derived is in good agreement with that inferred from ROSAT
X-ray observation out to 180 kpc. Within 30 kpc our mass is also consistent
with that inferred from Chandra and XMM-Newton X-ray observations, while within
120 kpc it is about 20% smaller. The model velocity dispersion anisotropy beta
parameter for the globular clusters in M87 is small, varying from -0.2 at the
centre to 0.2 at 40 kpc, and gradually decreasing to zero at 120 kpc.Comment: 20 pages, 16 figures, Accepted by Ap
Unveiling a Rich System of Faint Dwarf Galaxies in the Next Generation Fornax Survey
We report the discovery of 158 previously undetected dwarf galaxies in the
Fornax cluster central regions using a deep coadded and -band image
obtained with the DECam wide-field camera mounted on the 4-meter Blanco
telescope at the Cerro Tololo Interamerican Observatory as part of the {\it
Next Generation Fornax Survey} (NGFS). The new dwarf galaxies have
quasi-exponential light profiles, effective radii kpc and
average effective surface brightness values mag
arcsec. We confirm the existence of ultra-diffuse galaxies (UDGs) in the
Fornax core regions that resemble counterparts recently discovered in the Virgo
and Coma galaxy clusters.~We also find extremely low surface brightness NGFS
dwarfs, which are several magnitudes fainter than the classical UDGs. The
faintest dwarf candidate in our NGFS sample has an absolute magnitude of
\,mag. The nucleation fraction of the NGFS dwarf galaxy sample
appears to decrease as a function of their total luminosity, reaching from a
nucleation fraction of at luminosities brighter than
mag to at luminosities fainter than
mag. The two-point correlation function analysis of the
NGFS dwarf sample shows an excess on length scales below kpc,
pointing to the clustering of dwarf galaxies in the Fornax cluster core.Comment: 6 pages, 3 figures. Accepted for publication in The Astrophysical
Journal Letters. Download the high-resolution version of the paper from the
following link: https://www.dropbox.com/s/xb9vz8s29wlzjgf/ms.pdf?dl=
The Next Generation Virgo Cluster Survey. X. Properties of Ultra-Compact Dwarfs in the M87, M49 and M60 Regions
We use imaging from the Next Generation Virgo cluster Survey (NGVS) to
present a comparative study of ultra-compact dwarf (UCD) galaxies associated
with three prominent Virgo sub-clusters: those centered on the massive,
red-sequence galaxies M87, M49 and M60. We show how UCDs can be selected with
high completeness using a combination of half-light radius and location in
color-color diagrams ( or ). Although the central galaxies in
each of these sub-clusters have nearly identical luminosities and stellar
masses, we find large differences in the sizes of their UCD populations, with
M87 containing ~3.5 and 7.8 times more UCDs than M49 and M60, respectively. The
relative abundance of UCDs in the three regions scales in proportion to
sub-cluster mass, as traced by X-ray gas mass, total gravitating mass, number
of globular clusters, and number of nearby galaxies. We find that the UCDs are
predominantly blue in color, with ~85% of the UCDs having colors similar to
blue GCs and stellar nuclei of dwarf galaxies. We present evidence that UCDs
surrounding M87 and M49 may follow a morphological sequence ordered by the
prominence of their outer, low surface brightness envelope, ultimately merging
with the sequence of nucleated low-mass galaxies, and that envelope prominence
correlates with distance from either galaxy. Our analysis provides evidence
that tidal stripping of nucleated galaxies is an important process in the
formation of UCDs.Comment: 37 pages, 40 figures. To appear in The Astrophysical Journa
The Next Generation Virgo Cluster Survey. VI. The Kinematics of Ultra-compact Dwarfs and Globular Clusters in M87
The origin of ultra-compact dwarfs (UCDs)--objects larger and more massive
than typical globular clusters (GCs), but more compact than typical dwarf
galaxies--has been hotly debated in the 15 years since their discovery. Even
whether UCDs should be considered galactic in origin, or simply the most
extreme GCs, is not yet settled. We present the dynamical properties of 97
spectroscopically confirmed UCDs (rh >~10 pc) and 911 GCs associated with
central cD galaxy of the Virgo cluster, M87. Our UCDs, of which 89% have M_star
> ~2X10^6 M_sun and 92% are as blue as the classic blue GCs, nearly triple the
sample of previous confirmed Virgo UCDs, providing by far the best opportunity
for studying the global dynamics of a UCD system. We found that (1) UCDs have a
surface number density profile that is shallower than that of the blue GCs in
the inner ~ 70 kpc and as steep as that of the red GCs at larger radii; (2)
UCDs exhibit a significantly stronger rotation than the GCs, and the blue GCs
seem to have a velocity field that is more consistent with that of the
surrounding dwarf ellipticals than with that of UCDs; (3) UCDs have a radially
increasing orbital anisotropy profile, and are tangentially-biased at radii < ~
40 kpc and radially-biased further out. In contrast, the blue GCs become more
tangentially-biased at larger radii beyond ~ 40 kpc; (4) GCs with M_star >
2X10^6 M_sun have rotational properties indistinguishable from the less massive
ones, suggesting that it is the size, instead of mass, that differentiates UCDs
from GCs as kinematically distinct populations. We conclude that most UCDs in
M87 are not consistent with being merely the most luminous and extended
examples of otherwise normal GCs. The radially-biased orbital structure of UCDs
at large radii is in general agreement with the "tidally threshed dwarf galaxy"
scenario.Comment: 27 pages, 21 figures. To appear in The Astrophysical Journa
Multiwavelength Study of the Starburst Galaxy NGC 7714. II: The Balance between Young, Intermediate Age and Old Stars
We combine existing multiwavelength data (incl. an HST/GHRS UV spectrum, an
optical spectrum, far-IR, Xray and radio fluxes) with new HST/WFPC2 images,
near-IR photometry and K band spectroscopy. We use these data to constrain the
young, the intermediate age and the old stellar populations in the central 330
pc of the starburst galaxy NGC 7714. [...]
We find that the young burst responsible for the UV light is only a small
part of an extended episode of enhanced star formation (SF) [...]. The mass of
young and intermediate age stars thus formed equals at least 10% of the mass
locked in pre-existing stars of the underlying galaxy nucleus [...]. The
spectrophotometric SF timescale is long compared to the ~110 Myr elapsed since
closest contact with NGC 7715. The trigger of the starburst remains elusive.
NGC 7714 owes its brightness in the UV to a few low extinction lines of sight
towards young stars. [...] The different extinction estimates obtained from
different indicators result naturally from the coexistence of populations with
various ages and obscurations. The near-IR continuum image looks smoothest, as
a consequence of lower sensitivity to extinction and of a larger contribution
of old stars. We compare the nuclear properties of NGC 7714 with results from
studies in larger apertures. We emphasize that the global properties of
starburst galaxies are the result of the averaging over many lines of sight
with diverse properties in terms of obscuration and stellar ages.Comment: 29 pages (+20 figures and tables), Latex2e (figs. included), uses
aastex.cls. To be published in ApJ (May 2001 issue
The X-shooter Spectral Library (XSL): Data Release 3
We present the third data release (DR3) of the X-shooter Spectral Library
(XSL). This moderate-to-high resolution, near-ultraviolet-to-near-infrared
( nm, R 10 000) spectral library is composed of 830 stellar
spectra of 683 stars. DR3 improves upon the previous data release by providing
the combined de-reddened spectra of the three X-shooter segments over the full
nm wavelength range. It also includes additional 20 M-dwarf spectra
from the ESO archive. We provide detailed comparisons between this library and
Gaia EDR3, MILES, NGSL, CaT library, and (E-)IRTF. The normalised rms deviation
is better than or 5 for the majority of spectra in common between
MILES (144 spectra of 180), NGSL (112116), and (E-)IRTF (5577) libraries.
Comparing synthetic colours of those spectra reveals only negligible offsets
and small rms scatter, such as the median offset(rms) 0.0010.040 mag in
the (box1-box2) colour of the UVB arm,-0.0040.028 mag in (box3-box4) of
the VIS arm, and -0.0010.045 mag in (box2-box3) colour between the UVB and
VIS arms, when comparing stars in common with MILES. We also find an excellent
agreement between the Gaia published (BP-RP) colours and those measured from
the XSL DR3 spectra, with a zero median offset and an rms scatter of 0.037 mag
for 449 non-variable stars. The unmatched characteristics of this library,
which combine a relatively high resolution, a large number of stars, and an
extended wavelength coverage, will help us to bridge the gap between the
optical and the near-IR studies of intermediate and old stellar populations,
and to probe low-mass stellar systems.Comment: 26 pages, 25 figures, accepted to Astronomy & Astrophysics. The data
are available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr(130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ or on the XSL web-page
http://xsl.astro.unistra.f
Rôle des étoiles de la branche asymptotique des géantes dans les populations stellaires
STRASBOURG-Sc. et Techniques (674822102) / SudocMEUDON-Observatoire (920482302) / SudocSudocFranceF
The star formation history of Virgo spiral galaxies. Combined spectral and photometric inversion.
This thesis investigates the influence of ram pressure stripping on the star formation history of cluster spiral galaxies. Ram pressure stripping is the hydrodynamical interaction between the interstellar medium (ISM) of a spiral galaxy that is moving inside the potential well of a cluster, and the intracluster medium (ICM). If the dynamical pressure exerted by the ICM is larger than the restoring force due to the galactic potential, the galaxy loses gas from the outer disk. The Virgo cluster is an ideal laboratory to study environmental effects on galaxy evolution, because it is rich in spirals and dynamically young. From observations we know that the amount of atomic gas in Virgo spirals is less than that of galaxies in the field. In particular cluster spirals show truncated HI disks. For those galaxies that also show a symmetrical stellar distribution, ram pressure stripping is the most probably origin of the gas-disk truncation.Cette these etudie l'influence du balayage par pression dynamique sur l'histoire de la formation stellaire des galaxies spirales qui se trouvent dans des amas. Le balayage par pression dynamique est l'interaction hydrodynamique entre le milieu interstellaire (ISM) d'une galaxie spirale qui evolue dans le puits de potentiel d'un amas, et le milieu intra-amas (ICM). Si la pression dynamique exercee par l'ICM excede la force d'attraction gravitationnelle due au potentiel galactique, la galaxie perd du gaz de sa partie externe. L'amas de la Vierge constitue un laboratoire ideal pour etudier les effets de l'environnement sur l'evolution des galaxies. En effet, cet amas est riche en spirales et dynamiquement jeune. Des observations nous montrent que la quantite de gaz atomique qui se trouve dans les spirales de la Vierge est moins importante que celle des galaxies du champ. En particulier, les spirales des amas presentent des disques HI tronques. Pour celles des galaxies qui presentent aussi une distribution stellaire symetrique, le balayage par pression dynamique semblerait etre l'origine la plus probable de la troncature du gaz du disque