353 research outputs found
Nuclear star formation in the quasar PG1126-041 from adaptive optics assisted spectroscopy
We present adaptive optics assisted spectroscopy of three quasars obtained
with NACO at VLT. The high angular resolution achieved with the adaptive optics
(~0.08"), joined to the diagnostic power of near-IR spectroscopy, allow us to
investigate the properties of the innermost 100 pc of these quasars. In the
quasar with the best adaptive optics correction, PG1126-041, we spatially
resolve the Pa-alpha emission within the nuclear 100 pc. The comparison with
higher excitation lines suggests that the narrow Pa-alpha emission is due to
nuclear star formation. The inferred intensity of the nuclear star formation
(13 M(sun)/yr) may account for most of the far-IR luminosity observed in this
quasar.Comment: 4 pages, 4 figures. Accepted for publication in A&
Integral field spectroscopy in the near infrared of NGC 3125-A and SBS 0335-052
We present integral field spectroscopy in the near infrared of the nearby
dwarf starburst galaxies NGC 3125-A and of the low metallicity dwarf galaxy SBS
0335-052. The use of adaptive optics in the observations produces sub-arcsecond
angular resolution. We pinpoint the star forming cores of both galaxies,
identify relevant ISM components such as dust, photo ionized gas, shock excited
gas and molecular gas. We relate these components to the large scale star
formation process of the galaxies. In particular we find the emission of the
near infrared lines of H2 and especially [FeII] does not coincide with the HII
region in NGC 3125. We have the first clear detection of [FeII] in SBS
0335-052
LSD: Lyman-break galaxies Stellar populations and Dynamics. I: Mass, metallicity and gas at z~3.1
We present the first results of a project, LSD, aimed at obtaining
spatially-resolved, near-infrared spectroscopy of a complete sample of
Lyman-Break Galaxies at z~3. Deep observations with adaptive optics resulted in
the detection of the main optical lines, such as [OII], Hbeta and [OIII], which
are used to study sizes, SFRs, morphologies, gas-phase metallicities, gas
fractions and effective yields. Optical, near-IR and Spitzer/IRAC photometry is
used to measure stellar mass. We obtain that morphologies are usually complex,
with the presence of several peaks of emissions and companions that are not
detected in broad-band images. Typical metallicities are 10-50% solar, with a
strong evolution of the mass-metallicity relation from lower redshifts. Stellar
masses, gas fraction, and evolutionary stages vary significantly among the
galaxies, with less massive galaxies showing larger fractions of gas. In
contrast with observations in the local universe, effective yields decrease
with stellar mass and reach solar values at the low-mass end of the sample.
This effect can be reproduced by gas infall with rates of the order of the
SFRs. Outflows are present but are not needed to explain the mass-metallicity
relation. We conclude that a large fraction of these galaxies are actively
creating stars after major episodes of gas infall or merging.Comment: MNRAS, in pres
Metallicity evolution, metallicity gradients and gas fractions at z~3.4
We used near-infrared integral field spectroscopic observations from the
AMAZE and LSD programs to constrain the metallicity in a sample of 40 star
forming galaxies at 3<z<5 (most of which at z~3.4). We measure metallicities by
exploiting strong emission line diagnostics. We found that a significant
fraction of star-forming galaxies at z~3.4 deviate from the Fundamental
Metallicity Relation (FMR), with a metallicity up to a factor of ten lower than
expected according to the FMR. This deviation does not correlate with the
dynamical properties of the galaxy or with the presence of interactions. To
investigate the origin of the metallicity deviations in more detail, we also
infer information on the gas content, by inverting the Schmidt-Kennicutt
relation. In agreement with recent CO observational data, we found that, in
contrast with the steeply rising trend at 0<z<2, the gas fraction in massive
galaxies remains constant, with indication of a marginal decline, at 2<z<3.5.
When combined with the metallicity information, we infer that to explain both
the low metallicity and gas content in z~3.4 galaxies, both prominent outflows
and massive pristine gas inflows are needed. In ten galaxies we can also
spatially resolve the metallicity distribution. We found that the metallicity
generally anticorrelates with the distribution of star formation and with the
gas surface density. We discuss these findings in terms of pristine gas inflows
towards the center, and outflows of metal rich gas from the center toward the
external regions. (Abridged)Comment: Replaced to match the published versio
Constraint on the Assembly and Dynamics of Galaxies. II. Properties of Kiloparsec-Scale Clumps in Rest-Frame Optical Emission of z ~ 2 Star-Forming Galaxies
We study the properties of luminous stellar "clumps" identified in deep, high-resolution Hubble Space Telescope NIC2/F160W imaging at 1.6 μm of six z ~ 2 star-forming galaxies with existing near-infrared integral field spectroscopy from SINFONI at the Very Large Telescope. Individual clumps contribute ~0.5%-15% of the galaxy-integrated rest-frame ≈5000 Å emission, with median of ≈2%; the total contribution of clump light ranges from 10% to 25%. The median intrinsic clump size and stellar mass are ~1 kpc and ~10^9 M_☉, in the ranges for clumps identified in rest-UV or line emission in other studies. The clump sizes and masses in the subset of disks are broadly consistent with expectations for clump formation through gravitational instabilities in gas-rich, turbulent disks given the host galaxies' global properties. By combining the NIC2 data with Advanced Camera for Surveys (ACS)/F814W imaging available for one source, and adaptive-optics-assisted SINFONI Hα data for another, we infer modest color, M/L, and stellar age variations within each galaxy. In these two objects, sets of clumps identified at different wavelengths do not fully overlap; NIC2-identified clumps tend to be redder/older than ACS- or Hα-identified clumps without rest-frame optical counterparts. There is evidence for a systematic trend of older ages at smaller galactocentric radii among the clumps, consistent with scenarios where inward migration of clumps transports material toward the central regions. From constraints on a bulge-like component at radii ≾1-3 kpc, none of the five disks in our sample appears to contain a compact massive stellar core, and we do not discern a trend of bulge stellar mass fraction with stellar age of the galaxy. Further observations are necessary to probe the buildup of stellar bulges and the role of clumps in this process
Gas accretion as the origin of chemical abundance gradients in distant galaxies
It has recently been suggested that galaxies in the early Universe can grow
through the accretion of cold gas, and that this may have been the main driver
of star formation and stellar mass growth. Because the cold gas is essentially
primordial, it has a very low abundance of elements heavier than helium
(metallicity). As it is funneled to the centre of a galaxy, it will lead the
central gas having an overall lower metallicity than gas further from the
centre, because the gas further out has been enriched by supernovae and stellar
winds, and not diluted by the primordial gas. Here we report chemical
abundances across three rotationally-supported star-forming galaxies at z~3,
only 2 Gyr after the Big Bang. We find an 'inverse' gradient, with the central,
star forming regions having a lower metallicity than less active ones, opposite
to what is seen in local galaxies. We conclude that the central gas has been
diluted by the accretion of primordial gas, as predicted by 'cold flow' models.Comment: To Appear in Nature Oct 14, 2010; Supplementary Information included
her
Discovery of two infrared supernovae: a new window on the SN search
We report the discovery of two supernovae (SN 1999gw and SN 2001db) obtained
within the framework of an infrared monitoring campaign of Luminous Infrared
Galaxies, aimed at detecting obscured supernovae. SN 2001db, extinguished by
Av~5.5 mag, is the first supernova discovered in the infrared which has
received the spectroscopic confirmation. This result highlights the power of
infrared monitoring in detecting obscured SNe and indicates that optical
surveys are probably missing a significant fraction of SNe, especially in
obscured systems such as starburst galaxies. The preliminary estimate of SN
rate in LIRG galaxies is about an order of magnitude higher than that expected
from optical surveys.Comment: 9 pages, 7 figures, accepted for publication in A&
Strongly star-forming rotating disks in a complex merging system at z = 4,7 as revealed by ALMA
We performed a kinematical analysis of the [CII] line emission of the BR
1202-0725 system at z~4,7 using ALMA observations. The most prominent sources
of this system are a quasar and a submillimeter galaxy, separated by a
projected distance of about 24 kpc and characterized by very high SFR, higher
than 1000 Msun/yr. However, the ALMA observations reveal that these galaxies
apparently have undisturbed rotating disks, which is at variance with the
commonly accepted scenario in which strong star formation activity is induced
by a major merger. We also detected faint components which, after spectral
deblending, were spatially resolved from the main QSO and SMG emissions. The
relative velocities and positions of these components are compatible with
orbital motions within the gravitational potentials generated by the QSO host
galaxy and the SMG, suggesting that they are smaller galaxies in interaction or
gas clouds in accretion flows of tidal streams. We did not find any clear
spectral evidence for outflows caused by AGN or stellar feedback. This suggests
that the high star formation rates might be induced by interactions or minor
mergers with these companions, which do not affect the large-scale kinematics
of the disks, however. Our kinematical analysis also indicates that the QSO and
the SMG have similar Mdyn, mostly in the form of molecular gas, and that the
QSO host galaxy and the SMG are seen close to face-on with slightly different
disk inclinations: the QSO host galaxy is seen almost face-on (i~15), while the
SMG is seen at higher inclinations (i~25). Finally, the ratio between the black
hole mass of the QSO, obtained from XShooter spectroscopy, and the Mdyn of the
host galaxy is similar to value found in very massive local galaxies,
suggesting that the evolution of black hole galaxy relations is probably better
studied with dynamical than with stellar host galaxy masses.Comment: Accepted for publication in Astronomy and Astrophysic
The dust-to-stellar mass ratio as a valuable tool to probe the evolution of local and distant star forming galaxies
The survival of dust grains in galaxies depends on various processes. Dust can be produced in stars, it can grow in the interstellar medium and be destroyed by astration and interstellar shocks. In this paper, we assemble a few data samples of local and distant star-forming galaxies to analyse various dust-related quantities in low- and high-redshift galaxies, and to study how the relations linking the dust mass to the stellar mass and star formation rate evolve with redshift. We interpret the available data by means of chemical evolution models for discs and proto-spheroid (PSPH) starburst galaxies. In particular, we focus on the dust-to-stellar mass (DTS) ratio, as this quantity represents a true measure of how much dust per unit stellar mass survives the various destruction processes in galaxies and is observable. The theoretical models outline the strong dependence of this quantity on the underlying star formation history. Spiral galaxies are characterized by a nearly constant DTS as a function of the stellar mass and cosmic time, whereas PSPHs present an early steep increase of the DTS, which stops at a maximal value and decreases in the latest stages. In their late starburst phase, these models show a decrease of the DTS with their mass, which allows us to explain the observed anti-correlation between the DTS and the stellar mass. The observed redshift evolution of the DTS ratio shows an increase from z ∼ 0 to z ∼ 1, followed by a roughly constant behaviour at 1 ≲ z ≲ 2.5. Our models indicate a steep decrease of the global DTS at early times, which implies an expected decrease of the DTS at larger redshift.PS acknowledges financial support from the European Union's Seventh Framework Programme ASTRODEEP (FP7/2007- 2013), grant agreement no. 312725
AO assisted spectroscopy with SINFONI: PSF, background, and interpolation
I discuss 3 widely applicable aspects concerning calibration of the near
infrared adaptive optics integral field spectrometer SINFONI: (1) the accuracy
with which one needs to quantify the PSF and how this might be achieved in
practice; (2) how it is possible to fine tune the background subtraction to
minimise the residual OH airglow; and (3) how an altered perspective on
calibration data might lead to improvements in interpolation and greater
flexibility in reconstructing datacubes.Comment: 9 pages, invited contribution to the 2007 ESO Instrument Calibration
Worksho
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