1,128 research outputs found
PRUSSIC I - a JVLA survey of HCN/HCO+/HNC (1-0) emission in z3 dusty galaxies: Low dense-gas fractions in high-redshift star-forming galaxies
Dusty star-forming galaxies (DSFGs) at redshift z1 are among the most
vigorously star-forming galaxies in the Universe. However, their dense
(10 cm ) gas phase - typically traced by HCN(1-0) - remains
almost entirely unexplored: only two DSFGs have been detected in HCN(1-0) to
date. We present results of a JVLA survey of the J=1-0 transition of HCN, HCO+,
and HNC(1-0) in six strongly lensed DSFGs at z = 2.5 - 3.3, effectively
doubling the number of DSFGs with deep observations of these lines. We detect
HCN(1-0) emission in one source (J1202+5354, 4.4), with a tentative
HCO+ (1-0) detection in another (J1609+6045, 3.3). Spectral stacking
yields strict upper limits on the HCN/FIR (3.610) and
HCN/CO(1-0) ratios (0.045). The inferred HCN/FIR ratios (a proxy for the
star-formation efficiency) are consistent with those in z0 FIR-luminous
starbursts. However, the HCN/CO ratios - a proxy for the dense-gas fraction -
are a factor of a few lower than suggested by the two previous DSFG detections.
Our results imply that most DSFGs have low dense-gas fractions. A comparison
with Krumholz & Thompson (2007) models of star-forming galaxies indicates that
the bulk of gas in DSFGs is at lower densities (10 cm ),
similar to "normal" star-forming galaxies, rather than ultraluminous
starbursts.Comment: Submitted to A&A 28th April 2022, accepted 19th July 202
Mid-infrared diagnostics of starburst galaxies: clumpy, dense structures in star-forming regions in the Antennae (NGC 4038/4039)
Recently, mid-infrared instruments have become available on several large
ground-based telescopes, resulting in data sets with unprecedented spatial
resolution at these long wavelengths. In this paper we examine
'ground-based-only' diagnostics, which can be used in the study of star-forming
regions in starburst galaxies. By combining output from the stellar population
synthesis code Starburst 99 with the photoionization code Mappings, we model
stellar clusters and their surrounding interstellar medium, focusing on the
evolution of emission lines in the N- and Q-band atmospheric windows (8-13 and
16.5-24.5 micron respectively) and those in the near-infrared. We address the
detailed sensitivity of various emission line diagnostics to stellar population
age, metallicity, nebular density, and ionization parameter. Using our model
results, we analyze observations of two stellar clusters in the overlap region
of the Antennae galaxies obtained with VLT Imager and Spectrometer for mid
Infrared (VISIR). We find evidence for clumpy, high density, ionized gas. The
two clusters are young (younger than 2.5 and 3 Myr respectively), the
surrounding interstellar matter is dense (10^4 cm^-3 or larger) and can be
characterized by a high ionization parameter (logU > -1.53). Detailed analysis
of the mid-infrared spectral features shows that a (near-)homogeneous medium
cannot account for the observations, and that complex structure on scales below
the resolution limit, containing several young stellar clusters embedded in
clumpy gas, is more likely.Comment: 24 pages, 16 figures (3 in color), accepted for publication in Ap
Automatic kelvin probe compatible with ultrahigh vacuum
This article describes a new type of in situ ultrahighâvacuum compatible kelvin probe based on a voiceâcoil driving mechanism. This design exhibits several advantages over conventional mechanical feedâthrough and (in situ) piezoelectric devices in regard to the possibility of multiple probe geometry, flexibility of probe geometry, amplitude of oscillation, and pure parallel vibration. Automatic setup and constant spacing features are achieved using a digitalâtoâanalog converter (DAC) steered offset potential. The combination of very low driver noise pickâup and dataâacquisition system (DAS) signal processing techniques results in a work function (wfâ ) resolution, under optimal conditions, of <0.1 meV. Due to its high surface sensitivity and compatibility with standard sample cleaning and analysis techniques this design has numerous applications in surface studies, e.g., adsorption kinetics, sample topography and homogeneity, sputter profiles, etc. For semiconductor specimens the high wf resolution makes it eminently suitable for surface photovoltage (SPV) spectroscopy
An extreme proto-cluster of luminous dusty starbursts in the early Universe
We report the identification of an extreme proto-cluster of galaxies in the
early Universe whose core (nicknamed Distant Red Core, DRC) is formed by at
least ten dusty star-forming galaxies (DSFGs), confirmed to lie at via detection of [CI](1-0), CO(6-5), CO(4-3),
CO(2-1) and emission lines, detected
using ALMA and ATCA. The spectroscopically-confirmed components of the
proto-cluster are distributed over a region
and have a collective obscured star-formation rate (SFR) of , considerably higher than has been seen before in any
proto-cluster of galaxies or over-densities of DSFGs at . Most of
the star formation is taking place in luminous DSFGs since no Ly
emitters are detected in the proto-cluster core, apart from a Ly blob
located next to one of the DRC dusty components and extending over . The total obscured SFR of the proto-cluster could rise to if all the members of an over-density
of bright DSFGs discovered around DRC in a wide-field LABOCA 870-m image
are part of the same structure. The total halo mass of DRC could be as high as
and could be the progenitor of a Coma-like
cluster at . The relatively short gas-depletion times of the DRC
components suggest either the presence of a mechanism able to trigger extreme
star formation simultaneously in galaxies spread over a few hundred kpc or the
presence of gas flows from the cosmic web able to sustain star formation over
several hundred million years.Comment: Submitted to ApJ. Minor updates added, including a change of the
source name. Comments welcom
Faint InfraRed Extragalactic Survey: Data and Source Catalogue of the MS1054-03 field
We present deep near-infrared Js, H, and Ks band imaging of a field around
MS1054-03, a massive cluster at z=0.83. The observations were carried out with
ISAAC at the ESO VLT as part of the Faint InfraRed Extragalactic Survey
(FIRES). The total integration time amounts to 25.9h in Js, 24.4h in H, and
26.5h in Ks, divided nearly equally between four pointings covering 5.5'x5.3'.
The 3-sigma total limiting AB magnitudes for point sources from the shallowest
to deepest pointing are Js=26.0-26.2, H=25.5-25.8, and Ks=25.3-25.7. The
effective spatial resolution of the coadded images has FWHM=0.48", 0.46", and
0.52" in Js, H, and Ks. We complemented the ISAAC data with deep optical
imaging using existing HST WFPC2 mosaics in the F606W and F814W filters and new
U, B and V band data from VLT FORS1. We constructed a Ks-band limited
multicolour source catalogue to Ks(total,AB)=25 (about 5-sigma for point
sources). The catalogue contains 1858 objects, of which 1663 have eight-band
photometry. We describe the observations, data reduction, source detection and
photometric measurements method. We present the number counts, colour
distributions, and photometric redshifts z_ph of the catalogue sources. We find
that our counts at the faint end 22<Ks(AB)<25, with slope dlog(N)/dm=0.20, lie
at the flatter end of published counts in other deep fields and are consistent
with those we derived in the HDF-South, the other FIRES field. Spectroscopic
redshifts z_sp are available for about 330 sources in the MS1054-03 field;
comparison between the z_ph and z_sp shows very good agreement, with
=0.078. The MS1054-03 field observations complement our
HDF-South data set with nearly five times larger area at about 0.7 brighter
magnitudes. [ABRIDGED]Comment: Accepted for publication in the Astronomical Journal. 32 pages, 14
b/w figures, 1 color figur
A Substantial Population of Red Galaxies at z > 2: Modeling of the Spectral Energy Distributions of an Extended Sample
We investigate the nature of the substantial population of high-z galaxies
with Js-Ks>2.3 discovered as part of our FIRES survey. This colour cut
efficiently isolates z>2 galaxies with red rest-frame optical colors ("Distant
Red Galaxies" or DRGs). We select objects in the 2.5'x2.5' HDF-South (HDF-S)
and 5'x5' field around the MS1054-03 cluster; the surface densities at Ks<21
are 1.6+-0.6 and 1.0+-0.2 arcmin^-2. We discuss the 34 DRGs at 2<z<3.5: 11 at
Ks<22.5 in HDF-S and 23 at Ks<21.7 in the MS1054-03 field. We analyze the SEDs
constructed from our deep near-infrared (NIR) and optical imaging from the ESO
VLT and HST. We develop diagnostics involving I-Js, Js-H, and H-Ks to argue
that the red NIR colors of DRGs cannot be attributed solely to extinction and
require for many an evolved stellar population with prominent Balmer/4000A
break. In the rest-frame, the optical colours of DRGs fall within the envelope
of normal nearby galaxies and the UV colours suggest a wide range in star
formation activity and/or extinction. This contrasts with the much bluer and
more uniform SEDs of Lyman break galaxies (LBGs). From evolutionary synthesis
models with constant star formation, solar metallicity, Salpeter IMF, and
Calzetti et al. extinction law, we derive for the HDF-S (MS1054-03 field) DRGs
median ages of 1.7(2.0) Gyr, A_V = 2.7(2.4) mag, stellar masses 0.8(1.6)x10^11
Msun, M/L_V = 1.2(2.3) Msun/LVsun, and SFR = 120(170) Msun/yr. Models assuming
declining SFRs with e-folding timescales of 10Myr-1Gyr generally imply younger
ages, lower A_V's and SFRs, but similar stellar masses within a factor of two.
Compared to LBGs at similar redshifts and rest-frame L_V's, DRGs are older,
more massive, and more obscured for any given star formation history.
[ABRIDGED]Comment: Accepted for publication in the Astrophysical Journal. 27 pages, 14
b/w figure
Observations of the Hubble Deep Field South with the Infrared Space Observatory - II. Associations and star formation rates
We present results from a deep mid-IR survey of the Hubble Deep Field South
(HDF-S) region performed at 7 and 15um with the CAM instrument on board ISO. We
found reliable optical/near-IR associations for 32 of the 35 sources detected
in this field by Oliver et al. (2002, Paper I): eight of them were identified
as stars, one is definitely an AGN, a second seems likely to be an AGN, too,
while the remaining 22 appear to be normal spiral or starburst galaxies. Using
model spectral energy distributions (SEDs) of similar galaxies, we compare
methods for estimating the star formation rates (SFRs) in these objects,
finding that an estimator based on integrated (3-1000um) IR luminosity
reproduces the model SFRs best. Applying this estimator to model fits to the
SEDs of our 22 spiral and starburst galaxies, we find that they are forming
stars at rates of ~1-100 M_sol/yr, with a median value of ~40M_sol/yr, assuming
an Einstein - de Sitter universe with a Hubble constant of 50 km/s/Mpc, and
star formation taking place according to a Salpeter (1955) IMF across the mass
range 0.1-100M_sol. We split the redshift range 0.0<z<0.6 into two equal-volume
bins to compute raw estimates of the star formation rate density contributed by
these sources, assuming the same cosmology and IMF as above and computing
errors based on estimated uncertainties in the SFRs of individual galaxies. We
compare these results with other estimates of the SFR density made with the
same assumptions, showing them to be consistent with the results of Flores et
al. (1999) from their ISO survey of the CFRS 1415+52 field. However, the
relatively small volume of our survey means that our SFR density estimates
suffer from a large sampling variance, implying that our results, by
themselves, do not place tight constraints on the global mean SFR density.Comment: Accepted for MNRAS. 23 pages, 10 figures (Figs. 4&6 included here as
low resolution JPEGS), latex, uses mn,epsfig. Further information and full
resolution versions of Figs 4&6 available at http://astro.ic.ac.uk/hdfs (v2:
full author list added
- âŠ