487 research outputs found
New search strategy for high z intervening absorbers: GRB021004, a pilot study
We present near-infrared narrow- and broad-band imaging of the field of
GRB021004, performed with ISAAC on the UT1 of the ESO Very Large Telescope. The
narrow-band filters were chosen to match prominent emission lines at the
redshift of the absorption-line systems found against the early-time afterglow
of GRB021004: [OIII] at z=1.38 and Halpha at z=1.60, respectively. For the
z=1.38 system we find an emission-line source at an impact parameter of 16",
which is somewhat larger than the typical impact parameters of a sample of MgII
absorbers at redshifts around unity. Assuming that this tentative
redshift-identification is correct, the star formation rate of the galaxy is 13
+- 2 Msun/year. Our study reaches star-formation rate limits (5 sigma) of 5.7
Msun/year at z=1.38, and 7.7 Msun/year at z=1.60. These limits correspond to a
depth of roughly 0.13 L*. Any galaxy counterpart of the absorbers nearer to the
line of sight either has to be fainter than this limit or not be an
emission-line source.Comment: 4 pages, 3 figures, accepted for publication in A&A letter
Spitzer infrared spectrometer 16μm observations of the GOODS fields
We present Spitzer 16μm imaging of the Great Observatories Origins Deep Survey (GOODS) fields. We survey
150 arcmin^2 in each of the two GOODS fields (North and South), to an average 3σ depth of 40 and 65 μJy,
respectively. We detect ~1300 sources in both fields combined. We validate the photometry using the 3–24μm
spectral energy distribution of stars in the fields compared to Spitzer spectroscopic templates. Comparison with
ISOCAM and AKARI observations in the same fields shows reasonable agreement, though the uncertainties are
large. We provide a catalog of photometry, with sources cross-correlated with available Spitzer, Chandra, and
Hubble Space Telescope data. Galaxy number counts show good agreement with previous results from ISOCAM
and AKARI with improved uncertainties. We examine the 16–24μm flux ratio and find that for most sources it
lies within the expected locus for starbursts and infrared luminous galaxies. A color cut of S_(16)/S_(24) > 1.4 selects
mostly sources which lie at 1.1 < z < 1.6, where the 24μm passband contains both the redshifted 9.7 μm silicate
absorption and the minimum between polycyclic aromatic hydrocarbon emission peaks. We measure the integrated
galaxy light of 16μm sources and find a lower limit on the galaxy contribution to the extragalactic background
light at this wavelength to be 2.2 ± 0.2 nW m^(−2) sr^(−1)
Star formation and dust obscuration in the tidally distorted galaxy NGC 2442
Abridged: We present a detailed investigation of the morphological
distribution and level of star formation and dust obscuration in the nearby
tidally distorted galaxy NGC2442. Spitzer images in the IR at 3.6, 4.5, 5.8,
8.0um, and 24um and GALEX images at 1500\AA{} and 2300\AA{} allow us to resolve
the galaxy on scales between 240-600pc. We supplement these with archival data
in the B, J, H, and K bands. We use the 8um, 24um and FUV (1500\AA) emission to
study the star formation rate (SFR). We find that globally, these tracers of
star formation give a range of results of ~6-11\msun/yr, with the
dust-corrected FUV giving the highest value of SFR. We can reconcile the UV and
IR-based estimates by adopting a steeper UV extinction curve that lies in
between the starburst (Calzetti) and SMC extinction curves. However, the
regions of highest SFR intensity along the spiral arms are consistent with a
starburst-like extinction. Overall, the level of star-formation we find is
higher than previously published for this galaxy, by about a factor of two,
which, contrary to previous conclusions, implies that the interaction that
caused the distorted morphology of NGC2442 likely also triggered increased
levels of star-formation activity. Outside of the spiral arms, we discover what
appears to be a superbubble, ~1.7kpc across in the IRAC images. Significant
H{\alpha}, UV and IR emission in the area also suggest vigorous ongoing
star-formation. A known, recent supernova (SN1999ga) is located at the edge of
this superbubble. Although speculative at this stage, this area suggests a
large star-forming region with a morphology shaped by generations of
supernovae. Lastly, we discover an 8um (PAH) circumnuclear ring with an ~0.8kpc
radius. The H{\alpha} emission is largely concentrated inside that ring and
shows a vague spiral structure in the rest of the galaxy.Comment: 16 pages, 13 figures, accepted for publication in Ap
Ultraluminous X-ray sources out to z~0.3 in the COSMOS field
Using Chandra observations we have identified a sample of seven off-nuclear
X-ray sources, in the redshift range z=0.072-0.283, located within optically
bright galaxies in the COSMOS Survey. Using the multi-wavelength coverage
available in the COSMOS field, we study the properties of the host galaxies of
these ULXs. In detail, we derived their star formation rate from H_alpha
measurements and their stellar masses using SED fitting techniques with the aim
to compute the probability to have an off-nuclear source based on the host
galaxy properties. We divide the host galaxies in different morphological
classes using the available ACS/HST imaging. We find that our ULXs candidates
are located in regions of the SFR versus M plane where one or more
off-nuclear detectable sources are expected. From a morphological analysis of
the ACS imaging and the use of rest-frame colours, we find that our ULXs are
hosted both in late and early type galaxies. Finally, we find that the fraction
of galaxies hosting a ULX ranges from ~0.5% to ~0.2% going from L[0.5-2 keV]=3
x 10^39 erg s^-1 to L[0.5-2 keV]= 2 x 10^40 erg s^-1.Comment: 10 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
A Census of the High-Density Molecular Gas in M82
We present a three-pointing study of the molecular gas in the starburst
nucleus of M82 based on 190 - 307 GHz spectra obtained with Z-Spec at the
Caltech Submillimeter Observatory. We present intensity measurements,
detections and upper limits, for 20 transitions, including several new
detections of CS, HNC, C2H, H2CO, and CH3CCH lines. We combine our measurements
with previously-published measurements at other frequencies for HCN, HNC, CS,
C34S, and HCO+ in a multi-species likelihood analysis constraining gas mass,
density and temperature, and the species' relative abundances. We find some 1.7
- 2.7 x 10^8 M_sun of gas with n_H2 between 1 - 6 x 10^4 cm^-3 and T > 50 K.
While the mass and temperature are comparable to values inferred from mid-J CO
transitions, the thermal pressure is a factor of 10 - 20 greater. The molecular
interstellar medium is largely fragmented and is subject to ultraviolet
irradiation from the star clusters. It is also likely subject to cosmic rays
and mechanical energy input from the supernovae, and is warmer on average than
the molecular gas in the massive star formation regions in the Milky Way. The
typical conditions in the dense gas in M82's central kpc appear unfavorable for
further star formation; if any appreciable stellar populations are currently
forming, they are likely biased against low mass stars, producing a top-heavy
initial mass function.Comment: 15 pages (using emulateapj.cls), 6 figures, Astrophysical Journal, in
pres
Far-IR/Submillimeter Spectroscopic Cosmological Surveys: Predictions of Infrared Line Luminosity Functions for z<4 Galaxies
Star formation and accretion onto supermassive black holes in the nuclei of
galaxies are the two most energetic processes in the Universe, producing the
bulk of the observed emission throughout its history. We simulated the
luminosity functions of star-forming and active galaxies for spectral lines
that are thought to be good spectroscopic tracers of either phenomenon, as a
function of redshift. We focused on the infrared (IR) and sub-millimeter
domains, where the effects of dust obscuration are minimal. Using three
different and independent theoretical models for galaxy formation and
evolution, constrained by multi-wavelength luminosity functions, we computed
the number of star-forming and active galaxies per IR luminosity and redshift
bin. We converted the continuum luminosity counts into spectral line counts
using relationships that we calibrated on mid- and far-IR spectroscopic surveys
of galaxies in the local universe. Our results demonstrate that future
facilities optimized for survey-mode observations, i.e., the Space Infrared
Telescope for Cosmology and Astrophysics (SPICA) and the Cerro Chajnantor
Atacama Telescope (CCAT), will be able to observe thousands of z>1 galaxies in
key fine-structure lines, e.g., [SiII], [OI], [OIII], [CII], in a
half-square-degree survey, with one hour integration time per field of view.
Fainter lines such as [OIV], [NeV] and H_2 (0-0)S1 will be observed in several
tens of bright galaxies at 1<z<2, while diagnostic diagrams of active-nucleus
vs star-formation activity will be feasible even for normal z~1 galaxies. We
discuss the new parameter space that these future telescopes will cover and
that strongly motivate their construction.Comment: Accepted for publication in The Astrophysical Journal on 20/10/2011,
17 pages, 13 figure
Perinatal Exposure to Low Levels of the Environmental Antiandrogen Vinclozolin Alters Sex-Differentiated Social Play and Sexual Behaviors in the Rat
In this study we examined the effects of exposure to the antiandrogenic fungicide vinclozolin (Vz) on the development of two sex-differentiated behaviors that are organized by the perinatal actions of androgens. Pregnant Long-Evans rats were administered a daily oral dose of 0, 1.5, 3, 6, or 12 mg/kg Vz from the 14th day of gestation through postnatal day (PND)3. The social play behavior of juvenile offspring was examined on PND22 and again on PND34 during play sessions with a same-sex littermate. After they reached adulthood, the male offspring were examined with the ex copula penile reflex procedure to assess erectile function. Vz did not produce any gross maternal or neonatal toxicity, nor did it reduce the anogenital distance in male pups. We observed no effects of Vz on play behavior on PND22. However, the 12-mg/kg Vz dose significantly increased play behavior in the male offspring on PND34 compared with controls. The most dramatic increases were seen with the nape contact and pounce behavior components of play. The Vz effect was more pronounced in male than in female offspring. As adults, male offspring showed a significant reduction of erections at all dose levels during the ex copula penile reflex tests. The 12-mg/kg dose was also associated with an increase in seminal emissions. These effects demonstrate that perinatal Vz disrupts the development of androgen-mediated behavioral functions at exposure levels that do not produce obvious structural changes or weight reductions in androgen-sensitive reproductive organs
Spitzer IRS 16 micron Observations of the GOODS Fields
We present Spitzer 16 micron imaging of the Great Observatories Origins Deep
Survey (GOODS) fields. We survey 150 square arcminutes in each of the two GOODS
fields (North and South), to an average 3 sigma depth of 40 and 65 micro-Jy
respectively. We detect about 1300 sources in both fields combined. We validate
the photometry using the 3-24 micron spectral energy distribution of stars in
the fields compared to Spitzer spectroscopic templates. Comparison with ISOCAM
and AKARI observations in the same fields show reasonable agreement, though the
uncertainties are large. We provide a catalog of photometry, with sources cross
correlated with available Spitzer, Chandra, and HST data. Galaxy number counts
show good agreement with previous results from ISOCAM and AKARI, with improved
uncertainties. We examine the 16 to 24 micron flux ratio and find that for most
sources it lies within the expected locus for starbursts and infrared luminous
galaxies. A color cut of S_{16}/S_{24}>1.4 selects mostly sources which lie at
1.1<z<1.6, where the 24 micron passband contains both the redshifted 9.7 micron
silicate absorption and the minimum between PAH emission peaks. We measure the
integrated galaxy light of 16 micron sources, and find a lower limit on the
galaxy contribution to the extragalactic background light at this wavelength to
be 2.2\pm 0.2$ nW m^{-2} sr^{-1}.Comment: Accepted for Publication in the AJ. 53 preprint pages, including 15
figures and 8 tables. Table 1-4 are truncated in the ms.tex but are included
in full in the tar file (and will be available in the online version of the
AJ
Reconciling the local galaxy population with damped Ly-alpha cross sections and metal abundances
A comprehensive analysis of 355 high-quality WSRT HI 21-cm line maps of
nearby galaxies shows that the properties and incident rate of Damped
Lyman-alpha (DLA) absorption systems observed in the spectra of high redshift
QSOs are in good agreement with DLAs originating in gas disks of galaxies like
those in the z~0 population. Comparison of low-z DLA statistics with the HI
incidence rate and column density distribution f(N) for the local galaxy sample
shows no evidence for evolution in the integral "cross section density" below
z~1.5, implying that there is no need for a hidden population of galaxies or HI
clouds to contribute significantly to the DLA cross section. Compared with z~4,
our data indicates evolution of a factor of two in the comoving density along a
line of sight. We find that dN/dz(z=0)=0.045 +/- 0.006. The idea that the local
galaxy population can explain the DLAs is further strengthened by comparing the
properties of DLAs and DLA galaxies with the expectations based on our analysis
of local galaxies. The distribution of luminosities of DLA host galaxies, and
of impact parameters between QSOs and the centres of DLA galaxies, are in good
agreement with what is expected from local galaxies. Approximately 87% of low z
DLA galaxies are expected to be fainter than L* and 37 per cent have impact
parameters less than 1'' at z=0.5. The analysis shows that some host galaxies
with very low impact parameters and low luminosities are expected to be missed
in optical follow up surveys. The well-known metallicity-luminosity relation in
galaxies, in combination with metallicity gradients in galaxy disks, cause the
expected median metallicity of low redshift DLAs to be low (~1/7 solar), which
is also in good agreement with observations of low z DLAs. (Abridged)Comment: 22 pages, 22 figures. Accepted for publication in MNRAS. Fixed typo
Physical conditions in the neutral interstellar medium at z=2.43 toward Q2348-011
We obtained a high-resolution VLT-UVES spectrum of the quasar Q2348-011 over
a wavelength range that covers most of the prominent metal and molecular
absorption lines from the log N(HI)=20.50+-0.10 damped Lyman-alpha system at
zabs=2.43. From the column density ratios and the relative populations of H2
rotational and CI fine-structure levels, we derive the physical conditions
(relative abundances, dust-depletion, particle density, kinetic temperature and
ionizing flux) and discuss physical conditions in the neutral phase. Molecular
hydrogen is detected in seven components in the first four rotational levels (J
= 0-3) of the vibrational ground state. Absorption lines of H2 J = 4 (resp. J =
5) are also detected in six (resp. two) of these components. This leads to a
total molecular fraction of log f = -1.69+0.37-0.58. We confirm the earlier
findings that there is a correlation between N(FeII)/N(SII) and N(SiII)/N(SII)
indicative of a dust-depletion pattern. Surprisingly, however, the depletion of
metals onto dust in the H2 components is not large in this system: [Fe/S] =
-0.8 to -0.1. The gas in H2-bearing components is found to be cold but still
hotter than similar gas in our Galaxy (T > 130 K, instead of typically 80 K).
and dense (n=100-200 cm^-3). There is an anti-correlation between the logarithm
of the photo-absorption rate, and log N(H2)/N(CI) derived for each H2
component. We show that this is mostly due to shielding effects and implies
that the photo- absorption rate is a good indicator of the physical conditions
in the gas. We find that the gas is immersed in a intense UV field, about one
order of magnitude higher than in the solar vicinity. The results suggest that
the gas in H2-bearing DLAs is clumpy, and star-formation occurs in the
associated object.Comment: 13 pages, 14 figures, accepted for publication in A&
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