287 research outputs found
CO map and steep Kennicutt-Schmidt relation in the extended UV disk of M63
Results from the UV satellite GALEX revealed large extensions of disks in
some nearby spiral galaxies, extending out to 3 to 4 times the isophotal
radius, r25. M63 is a remarkable example of a spiral galaxy with one of the
most extended UV disks, so it offers the opportunity to search for the
molecular gas and characterize the star formation in outer disk regions as
revealed by the UV emission. We obtained deep CO(1-0) and CO(2-1) observations
on the IRAM 30 m telescope along the major axis of the M63 disk from the center
out to the galactocentric radius rgal = 1.6 r25 and over a bright UV region at
rgal = 1.36 r25. CO(1-0) is detected all along the M63 major axis out to r25,
and CO(2-1) is confined to rgal = 0.68 r25, which may betray lower excitation
temperatures in the outer disk. CO(1-0) is also detected in the external bright
UV region of M63. The radial profiles of the CO emission and of the Halpha, 24
micron, NUV and FUV star formation tracers and HI taken from the literature
show a severe drop with the galactocentric radius, such that beyond r25 they
are all absent with the exception of a faint UV emission and HI. The CO
emission detection in the external UV region, where the UV flux is higher than
the UV flux observed beyond r25, highlights a tight correlation between the CO
and UV fluxes, namely the amount of molecular gas and the intensity of star
formation. This external UV region is dominated by the atomic gas, suggesting
that HI is more likely the precursor of H2 rather than the product of UV
photodissociation. A broken power law needs to be invoked to describe the
Kennicutt-Schmidt (K-S) relation of M63 from the center of the galaxy out to
rgal = 1.36 r25. While all along the major axis out to r25 the K-S relation is
almost linear, in the external UV region the SFR regime is highly nonlinear and
characterized by a steep K-S relation and very low star formation efficiency.Comment: 12 pages, 8 figures, A&A accepte
New constraints on dust emission and UV attenuation of z=6.5-7.5 galaxies from millimeter observations
We have targeted two recently discovered Lyman break galaxies (LBGs) to
search for dust continuum and [CII] 158 micron line emission. The strongly
lensed z~6.8 LBG A1703-zD1 behind the galaxy cluster Abell 1703, and the
spectroscopically confirmed z=7.508 LBG z8-GND-5296 in the GOODS-N field have
been observed with the Plateau de Bure interferometer (PdBI) at 1.2mm. These
observations have been combined with those of three z>6.5 Lya emitters (named
HCM6A, Himiko, and IOK-1), for which deep measurements were recently obtained
with the PdBI and ALMA. [CII] is undetected in both galaxies, providing a deep
upper limit for Abell1703-zD1, comparable to recent ALMA non-detections. Dust
continuum emission from Abell1703-zD1 and z8-GND-5296 is not detected with an
rms of 0.12 and 0.16 mJy/beam. From these non-detections we derive upper limits
on their IR luminosity and star formation rate, dust mass, and UV attenuation.
Thanks to strong gravitational lensing the limit for Abell1703-zD1 is probing
the sub-LIRG regime ( Lsun) and very low dust
masses ( Msun). We find that all five galaxies are
compatible with the Calzetti IRX- relation, their UV attenuation is
compatible with several indirect estimates from other methods (the UV slope,
extrapolation of the attenuation measured from the IR/UV ratio at lower
redshift, and SED fits), and the dust-to-stellar mass ratio is not incompatible
with that of galaxies from z=0 to 3. For their stellar mass the high-z galaxies
studied here have an attenuation below the one expected from the mean relation
of low redshift (z<1.5) galaxies. More and deeper (sub)-mm data are clearly
needed to directly determine the UV attenuation and dust content of the
dominant population of high-z star-forming galaxies and to establish more
firmly their dependence on stellar mass, redshift, and other properties.Comment: 10 pages, 7 figures. Minor revisions. Accepted for publication in A&
Resolving The ISM Surrounding GRBs with Afterglow Spectroscopy
We review current research related to spectroscopy of gamma-ray burst (GRB)
afterglows with particular emphasis on the interstellar medium (ISM) of the
galaxies hosting these high redshift events. These studies reveal the physical
conditions of star-forming galaxies and yield clues to the nature of the GRB
progenitor. We offer a pedagogical review of the experimental design and review
current results. The majority of sightlines are characterized by large HI
column densities, negligible molecular fraction, the ubiquitous detection of UV
pumped fine-structure transitions, and metallicities ranging from 1/100 to
nearly solar abundance.Comment: Conference procedings for Gamma Ray Bursts 2007 November 5-9, 2007
Santa Fe, New Mexico (8 pages, 4 figures
Signatures of Cool Gas Fueling a Star-Forming Galaxy at Redshift 2.3
Galaxies are thought to be fed by the continuous accretion of intergalactic
gas, but direct observational evidence has been elusive. The accreted gas is
expected to orbit about the galaxy's halo, delivering not just fuel for
star-formation but also angular momentum to the galaxy, leading to distinct
kinematic signatures. Here we report observations showing these distinct
signatures near a typical distant star-forming galaxy where the gas is detected
using a background quasar passing 26 kpc from the host. Our observations
indicate that gas accretion plays a major role in galaxy growth since the
estimated accretion rate is comparable to the star-formation rate.Comment: 33 pages, 8 figures, version matching the proofed tex
On the Nature of Velocity Fields in High z Galaxies
We analyze the gas kinematics of damped Lya systems (DLAs) hosting high z
gamma-ray bursts (GRBs) and those toward quasars (QSO-DLAs) focusing on
threestatistics: (1) dv, the velocity interval encompassing 90% of the
totaloptical depth, (2,3) Wsi and Wciv, the rest equivalent widths of the
SiII1526 and CIV1548 transitions. The dv distributions of the GRB-DLAs and
QSO-DLAs are similar, each has median dv~80km/s and a significant tail to
several hundred km/s. This suggests comparable galaxy masses for the parent
populations of GRB-DLAs and QSO-DLAs and we infer the average dark matter halo
mass of GRB galaxies is <~10^{12} Msol. The unique configuration of GRB-DLA
sightlines and the presence (and absence) of fine-structure absorption together
give special insight into the nature of high z, protogalactic velocity fields.
The data support a scenario where the dv statistic reflects dynamics in the
interstellar medium (ISM) and Wsi traces motions outside the ISM (e.g. halo
gas, galactic-scale winds). The Wsi statistic and gas metallicity [M/H] are
tightly correlated, especially for the QSO-DLAs: [M/H]=a + b log(Wsi/1A) with
a=-0.92+/-0.05 and b=-1.41+/-0.10. We argue that the Wsi statistic primarily
tracks dynamical motions in the halos of high z galaxies and interpret this
correlation as a mass-metallicity relation with very similar slope to the trend
observed in local, low-metallicity galaxies. Finally, the GRB-DLAs exhibit
systematically larger Wsi values (>0.5A) than the QSO-DLAs (~ 0.5A) which
may suggest galactic-scale outflows contribute to the largest observed velocity
fields.Comment: 14 pages, 9 figures. Submitted to Ap
Physics of a clumpy lensed galaxy at z=1.6
Observations have shown that massive star-forming clumps are present in the
internal structure of high-redshift galaxies. One way to study these clumps in
detail with a higher spatial resolution is by exploiting the power of strong
gravitational lensing which stretches images on the sky. In this work, we
present an analysis of the clumpy galaxy A68-HLS115 at , located
behind the cluster Abell 68, but strongly lensed by a cluster galaxy member.
Resolved observations with SINFONI/VLT in the near-infrared show Ha, Hb, [NII],
and [OIII] emission lines. Combined with images covering the B band to the
far-infrared and CO(2-1) observations, this makes this galaxy one of the only
sources for which such multi-band observations are available and for which it
is possible to study the properties of resolved star-forming clumps and to
perform a detailed analysis of the integrated properties, kinematics, and
metallicity. We obtain a stability of by
modeling the kinematics, which means that the galaxy is dominated by rotation,
but this ratio also indicates that the disk is marginally stable. We find a
high intrinsic velocity dispersion of km s that could be
explained by the high gas fraction of observed in this
galaxy. This high and the observed sSFR of
suggest that the disk turbulence and instabilities are mostly regulated by
incoming gas. The direct measure of the Toomre stability criterion of
could also indicate the presence of a quasi-stable thick disk.
Finally, we identify three clumps in the Ha map which have similar velocity
dispersions, metallicities, and seem to be embedded in the rotating disk. These
three clumps contribute together to on the SFR(Ha) of the galaxy and
show a SFR density about times higher than HII regions in the local
Universe.Comment: Accepted for publication in A&A. 10 pages, 7 figure
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