374 research outputs found
The WiFeS S7 AGN survey: Current status and recent results on NGC 6300
The Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7) is a
targeted survey probing the narrow-line regions (NLRs) of a representative
sample of ~140 nearby (z<0.02) Seyfert galaxies by means of optical integral
field spectroscopy. The survey is based on a homogeneous data set observed
using the Wide Field Spectrograph WiFeS. The data provide a 25x38 arcsec
field-of-view around the galaxy centre at typically ~1.5 arcsec spatial
resolution and cover a wavelength range between ~3400 - 7100 at spectral
resolutions of ~100 km s and ~50 km s in the blue and red parts,
respectively. The survey is primarily designed to study gas excitation and star
formation around AGN, with a special focus on the shape of the AGN ionising
continuum, the interaction between radio jets and the NLR gas, and the nature
of nuclear LINER emission. We provide an overview of the current status of
S7-based results and present new results for NGC 6300.Comment: 5 pages, 1 figure, Refereed Proceeding of the "The Universe of
Digital Sky Surveys" conference held at the INAF - Observatory of
Capodimonte, Naples, on 25th-28th november 2014, to be published on
Astrophysics and Space Science Proceedings, edited by Longo, Napolitano,
Marconi, Paolillo, Iodic
Interaction between vortices in models with two order parameters
The interaction energy and force between widely separated strings is analyzed
in a field theory having applications to superconducting cosmic strings, the
SO(5) model of high-temperature superconductivity, and solitons in nonlinear
optics. The field theory has two order parameters, one of which is broken in
the vacuum (giving rise to strings), the other of which is unbroken in the
vacuum but which could nonetheless be broken in the core of the string. If this
does occur, there is an effect on the energetics of widely separated strings.
This effect is important if the length scale of this second order parameter is
longer than that of the other fields in the problem.Comment: 11 pages, 3 figures. Minor changes in the text. Accepted for
publication in Phys. Rev.
Infrared color selection of massive galaxies at z > 3
We introduce a new color-selection technique to identify high-redshift,
massive galaxies that are systematically missed by Lyman-break selection. The
new selection is based on the H_{160} and IRAC 4.5um bands, specifically H -
[4.5] > 2.25 mag. These galaxies, dubbed "HIEROs", include two major
populations that can be separated with an additional J - H color. The
populations are massive and dusty star-forming galaxies at z > 3 (JH-blue) and
extremely dusty galaxies at z < 3 (JH-red). The 350 arcmin^2 of the GOODS-N and
GOODS-S fields with the deepest HST/WFC3 and IRAC data contain 285 HIEROs down
to [4.5] 3) HIEROs, which
have a median photometric redshift z ~4.4 and stellar massM_{*}~10^{10.6} Msun,
and are much fainter in the rest-frame UV than similarly massive Lyman-break
galaxies (LBGs). Their star formation rates (SFRs) reaches ~240 Msun yr^{-1}
leading to a specific SFR, sSFR ~4.2 Gyr^{-1}, suggesting that the sSFRs for
massive galaxies continue to grow at z > 2 but at a lower growth rate than from
z=0 to z=2. With a median half-light radius of 2 kpc, including ~20% as compact
as quiescent galaxies at similar redshifts, JH-blue HIEROs represent perfect
star-forming progenitors of the most massive (M_{*} > 10^{11.2} Msun) compact
quiescent galaxies at z ~ 3 and have the right number density. HIEROs make up
~60% of all galaxies with M_{*} > 10^{10.5} Msun identified at z > 3 from their
photometric redshifts. This is five times more than LBGs with nearly no overlap
between the two populations. While HIEROs make up 15-25% of the total SFR
density at z ~ 4-5, they completely dominate the SFR density taking place in
M_{*} >10^{10.5} Msun galaxies, and are therefore crucial to understanding the
very early phase of massive galaxy formation.Comment: ApJS, in pres
Combined CO & Dust Scaling Relations of Depletion Time and Molecular Gas Fractions with Cosmic Time, Specific Star Formation Rate and Stellar Mass
We combine molecular gas masses inferred from CO emission in 500 star forming
galaxies (SFGs) between z=0 and 3, from the IRAM-COLDGASS, PHIBSS1/2 and other
surveys, with gas masses derived from Herschel far-IR dust measurements in 512
galaxy stacks over the same stellar mass/redshift range. We constrain the
scaling relations of molecular gas depletion time scale (tdepl) and gas to
stellar mass ratio (Mmolgas/M*) of SFGs near the star formation main-sequence
with redshift, specific star formation rate (sSFR) and stellar mass (M*). The
CO- and dust-based scaling relations agree remarkably well. This suggests that
the CO-H2 mass conversion factor varies little within 0.6dex of the main
sequence (sSFR(ms,z,M*)), and less than 0.3dex throughout this redshift range.
This study builds on and strengthens the results of earlier work. We find that
tdepl scales as (1+z)^-0.3 *(sSFR/sSFR(ms,z,M*))^-0.5, with little dependence
on M*. The resulting steep redshift dependence of Mmolgas/M* ~(1+z)^3 mirrors
that of the sSFR and probably reflects the gas supply rate. The decreasing gas
fractions at high M* are driven by the flattening of the SFR-M* relation.
Throughout the redshift range probed a larger sSFR at constant M* is due to a
combination of an increasing gas fraction and a decreasing depletion time
scale. As a result galaxy integrated samples of the Mmolgas-SFR rate relation
exhibit a super-linear slope, which increases with the range of sSFR. With
these new relations it is now possible to determine Mmolgas with an accuracy of
0.1dex in relative terms, and 0.2dex including systematic uncertainties.Comment: ApJ accepte
A CANDELS WFC3 Grism Study of Emission-Line Galaxies at z~2: A Mix of Nuclear Activity and Low-Metallicity Star Formation
We present Hubble Space Telescope Wide Field Camera 3 slitless grism
spectroscopy of 28 emission-line galaxies at z~2, in the GOODS-S region of the
Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). The
high sensitivity of these grism observations, with 1-sigma detections of
emission lines to f > 2.5x10^{-18} erg/s/cm^2, means that the galaxies in the
sample are typically ~7 times less massive (median M_* = 10^{9.5} M_sun) than
previously studied z~2 emission-line galaxies. Despite their lower mass, the
galaxies have OIII/Hb ratios which are very similar to previously studied z~2
galaxies and much higher than the typical emission-line ratios of local
galaxies. The WFC3 grism allows for unique studies of spatial gradients in
emission lines, and we stack the two-dimensional spectra of the galaxies for
this purpose. In the stacked data the OIII emission line is more spatially
concentrated than the Hb emission line with 98.1 confidence. We additionally
stack the X-ray data (all sources are individually undetected), and find that
the average L(OIII)/L(0.5-10 keV) ratio is intermediate between typical z~0
obscured active galaxies and star-forming galaxies. Together the compactness of
the stacked OIII spatial profile and the stacked X-ray data suggest that at
least some of these low-mass, low-metallicity galaxies harbor weak active
galactic nuclei.Comment: ApJ accepted. 8 pages, 6 figure
The Redshift One LDSS-3 Emission line Survey (ROLES) II: Survey method and z~1 mass-dependent star-formation rate density
Motivated by suggestions of 'cosmic downsizing', in which the dominant
contribution to the cosmic star formation rate density (SFRD) proceeds from
higher to lower mass galaxies with increasing cosmic time, we describe the
design and implementation of the Redshift One LDSS3 Emission line Survey
(ROLES). ROLES is a K-selected (22.5 < K_AB < 24.0) survey for dwarf galaxies
[8.5<log(M*/Msun)< 9.5] at 0.89 < z < 1.15 drawn from two extremely deep fields
(GOODS-S and MS1054-FIRES). Using the [OII]3727 emission line, we obtain
redshifts and star-formation rates (SFRs) for star-forming galaxies down to a
limit of ~0.3 Msun/yr. We present the [OII] luminosity function measured in
ROLES and find a faint end slope of alpha_faint ~ -1.5, similar to that
measured at z~0.1 in the SDSS. By combining ROLES with higher mass surveys, we
measure the SFRD as a function of stellar mass using [OII] (with and without
various empirical corrections), and using SED-fitting to obtain the SFR from
the rest-frame UV luminosity for galaxies with spectroscopic redshifts. Our
best estimate of the corrected [OII]-SFRD and UV SFRD both independently show
that the SFRD evolves equally for galaxies of all masses between z~1 and z~0.1.
The exact evolution in normalisation depends on the indicator used, with the
[OII]-based estimate showing a change of a factor of ~2.6 and the UV-based a
factor of ~6. We discuss possible reasons for the discrepancy in normalisation
between the indicators, but note that the magnitude of this uncertainty is
comparable to the discrepancy between indicators seen in other z~1 works. Our
result that the shape of the SFRD as a function of stellar mass (and hence the
mass range of galaxies dominating the SFRD) does not evolve between z~1 and
z~0.1 is robust to the choice of indicator. [abridged]Comment: Resubmitted to MNRAS following first referee report. 20 pages, 16
figures. High resolution version available at
http://astro.uwaterloo.ca/~dgilbank/papers/roles2.pd
Geometrical tests of cosmological models. III. The cosmology-evolution diagram at z=1
The rotational velocity of distant galaxies, when interpreted as a size
(luminosity) indicator, may be used as a tool to select high redshift standard
rods (candles) and probe world models and galaxy evolution via the classical
angular diameter-redshift or Hubble diagram tests. We implement the proposed
testing strategy using a sample of 30 rotators spanning the redshift range
0.2<z<1 with high resolution spectra and images obtained by the VIMOS/VLT Deep
Redshift Survey (VVDS) and the Great Observatories Origins Deep Survey (GOODs).
We show that by applying at the same time the angular diameter-redshift and
Hubble diagrams to the same sample of objects (i.e. velocity selected galactic
discs) one can derive a characteristic chart, the cosmology-evolution diagram,
mapping the relation between global cosmological parameters and local
structural parameters of discs such as size and luminosity. This chart allows
to put constraints on cosmological parameters when general prior information
about discs evolution is available. In particular, by assuming that equally
rotating large discs cannot be less luminous at z=1 than at present (M(z=1) <
M(0)), we find that a flat matter dominated cosmology (Omega_m=1) is excluded
at a confidence level of 2sigma and an open cosmology with low mass density
(Omega_m = 0.3) and no dark energy contribution is excluded at a confidence
level greater than 1 sigma. Inversely, by assuming prior knowledge about the
cosmological model, the cosmology-evolution diagram can be used to gain useful
insights about the redshift evolution of the structural parameters of baryonic
discs hosted in dark matter halos of nearly equal masses.Comment: 14 pages and 11 figures. A&A in pres
The FMOS-COSMOS survey of star-forming galaxies at z~1.6 III. Survey design, performance, and sample characteristics
We present a spectroscopic survey of galaxies in the COSMOS field using the
Fiber Multi-Object Spectrograph (FMOS), a near-infrared instrument on the
Subaru Telescope. Our survey is specifically designed to detect the Halpha
emission line that falls within the H-band (1.6-1.8 um) spectroscopic window
from star-forming galaxies with 1.4 ~10^10 Msolar. With
the high multiplex capability of FMOS, it is now feasible to construct samples
of over one thousand galaxies having spectroscopic redshifts at epochs that
were previously challenging. The high-resolution mode (R~2600) effectively
separates Halpha and [NII]6585 thus enabling studies of the gas-phase
metallicity and photoionization state of the interstellar medium. The primary
aim of our program is to establish how star formation depends on stellar mass
and environment, both recognized as drivers of galaxy evolution at lower
redshifts. In addition to the main galaxy sample, our target selection places
priority on those detected in the far-infrared by Herschel/PACS to assess the
level of obscured star formation and investigate, in detail, outliers from the
star formation rate - stellar mass relation. Galaxies with Halpha detections
are followed up with FMOS observations at shorter wavelengths using the J-long
(1.11-1.35 um) grating to detect Hbeta and [OIII]5008 that provides an
assessment of extinction required to measure star formation rates not hampered
by dust, and an indication of embedded Active Galactic Nuclei. With 460
redshifts measured from 1153 spectra, we assess the performance of the
instrument with respect to achieving our goals, discuss inherent biases in the
sample, and detail the emission-line properties. Our higher-level data
products, including catalogs and spectra, are available to the community.Comment: 26 pages, Updated version resubmitted to ApJSS; Data products and
catalogs are now available at http://member.ipmu.jp/fmos-cosmos
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