508 research outputs found
VALES: IV. Exploring the transition of star formation efficiencies between normal and starburst galaxies using APEX/SEPIA Band-5 and ALMA at low redshift
In this work we present new APEX/SEPIA Band-5 observations targeting the CO
() emission line of 24 Herschel-detected galaxies at .
Combining this sample {with} our recent new Valpara\'iso ALMA Line Emission
Survey (VALES), we investigate the star formation efficiencies (SFEs =
SFR/) of galaxies at low redshift. We find the SFE of our sample
bridges the gap between normal star-forming galaxies and Ultra-Luminous
Infrared Galaxies (ULIRGs), which are thought to be triggered by different star
formation modes. Considering the as the SFR and the
ratio, our data show a continuous and smooth increment as a function of
infrared luminosity (or star formation rate) with a scatter about 0.5 dex,
instead of a steep jump with a bimodal behaviour. This result is due to the use
of a sample with a much larger range of sSFR/sSFR using LIRGs, with
luminosities covering the range between normal and ULIRGs. We conclude that the
main parameters controlling the scatter of the SFE in star-forming galaxies are
the systematic uncertainty of the conversion factor, the gas
fraction and physical size.Comment: 9pages, 7 figures, 1 table, accepted for publication in MNRA
Spitzer Observations of Low Luminosity Isolated and Low Surface Brightness Galaxies
We examine the infrared properties of five low surface brightness galaxies
(LSBGs) and compare them with related but higher surface brightness galaxies,
using Spitzer Space Telescope images and spectra. All the LSBGs are detected in
the 3.6 and 4.5um bands, representing the stellar population. All but one are
detected at 5.8 and 8.0um, revealing emission from hot dust and aromatic
molecules, though many are faint or point-like at these wavelengths. Detections
of LSBGs at the far-infrared wavelengths, 24, 70, and 160um, are varied in
morphology and brightness, with only two detections at 160um, resulting in
highly varied spectral energy distributions. Consistent with previous
expectations for these galaxies, we find that detectable dust components exist
for only some LSBGs, with the strength of dust emission dependent on the
existence of bright star forming regions. However, the far-infrared emission
may be relatively weak compared with normal star-forming galaxies.Comment: 20 pages, 8 figures, accepted to Ap
The Seyfert Population in the Local Universe
The magnitude-limited catalog of the Southern Sky Redshift Survey (SSRS2), is
used to characterize the properties of galaxies hosting Active Galactic Nuclei.
Using emission-line ratios, we identify a total of 162 (3%) Seyfert galaxies
out of the parent sample with 5399 galaxies. The sample contains 121 Seyfert 2
galaxies and 41 Seyfert 1. The SSRS2 Seyfert galaxies are predominantly in
spirals of types Sb and earlier, or in galaxies with perturbed appearance as
the result of strong interactions or mergers. Seyfert galaxies in this sample
are twice as common in barred hosts than the non-Seyferts. By assigning
galaxies to groups using a percolation algorithm we find that the Seyfert
galaxies in the SSRS2 are more likely to be found in binary systems, when
compared to galaxies in the SSRS2 parent sample. However, there is no
statistically significant difference between the Seyfert and SSRS2 parent
sample when systems with more than 2 galaxies are considered. The analysis of
the present sample suggests that there is a stronger correlation between the
presence of the AGN phenomenon with internal properties of galaxies
(morphology, presence of bar, luminosity) than with environmental effects
(local galaxy density, group velocity dispersion, nearest neighbor distance).Comment: 35 pages, 13 figures, Accepted to be publised in Astronomical Journa
Evolution of the dusty infrared luminosity function from z=0 to z=2.3 using observations from Spitzer
We derive the evolution of the infrared (IR) luminosity function (LF) over
the last 4/5ths of cosmic time, using deep 24um and 70um imaging of the GOODS
North and South fields. We use an extraction technique based on prior source
positions at shorter wavelengths to build the 24 and 70um source catalogs. The
majority (93%) of the sources have a spectroscopic (39%) or a photometric
redshift (54%) and, in our redshift range of interest (i.e., 1.3<z<2.3) ~20% of
the sources have a spectroscopic redshifts. To extend our study to lower 70um
luminosities we perform a stacking analysis and we characterize the observed
L_24/(1+z) vs L_70/(1+z) correlation. Using spectral energy distribution
templates which best fit this correlation, we derive the IR luminosity of
sources from their 24 and 70 um fluxes. We then compute the IR LF at
z=1.55+/-0.25 and z=2.05+/-0.25. The redshift evolution of the IR LF from z=1.3
to z=2.3 is consistent with a luminosity evolution proportional to
(1+z)^1.0+/-0.9 combined with a density evolution proportional to
(1+z)^-1.1+/-1.5. At z~2, luminous IR galaxies (LIRGs: 10^11Lsun< LIR
<10^12Lsun) are still the main contributors to the total comoving IR luminosity
density (IR LD) of the Universe. At z~2, LIRGs and ultra-luminous IR galaxies
(ULIRGs: 10^12Lsun< LIR) account for ~49% and ~17% respectively of the total IR
LD of the Universe. Combined with previous results for galaxies at z<1.3 and
assuming a constant conversion between the IR luminosity and star-formation
rate (SFR) of a galaxy, we study the evolution of the SFR density of the
Universe from z=0 to z=2.3. We find that the SFR density of the Universe
strongly increased with redshift from z=0 to z=1.3, but is nearly constant at
higher redshift out to z=2.3. As part of the online material accompanying this
article, we present source catalogs at 24um and 70um for both the GOODS-North
and -South fields.Comment: 19 pages, 14 figures. Accepted for publication in A&A. Online catalog
at CDS soo
X-Ray Groups of Galaxies in the Aegis Deep and Wide Fields
We present the results of a search for extended X-ray sources and their
corresponding galaxy groups from 800-ks Chandra coverage of the All-wavelength
Extended Groth Strip International Survey (AEGIS). This yields one of the
largest X-ray selected galaxy group catalogs from a blind survey to date. The
red-sequence technique and spectroscopic redshifts allow us to identify 100
of reliable sources, leading to a catalog of 52 galaxy groups. The groups span
the redshift range and virial mass range
. For the 49 extended
sources which lie within DEEP2 and DEEP3 Galaxy Redshift Survey coverage, we
identify spectroscopic counterparts and determine velocity dispersions. We
select member galaxies by applying different cuts along the line of sight or in
projected spatial coordinates. A constant cut along the line of sight can cause
a large scatter in scaling relations in low-mass or high-mass systems depending
on the size of cut. A velocity dispersion based virial radius can more
overestimate velocity dispersion in comparison to X-ray based virial radius for
low mass systems. There is no significant difference between these two radial
cuts for more massive systems. Independent of radial cut, overestimation of
velocity dispersion can be created in case of existence of significant
substructure and also compactness in X-ray emission which mostly occur in low
mass systems. We also present a comparison between X-ray galaxy groups and
optical galaxy groups detected using the Voronoi-Delaunay method (VDM) for
DEEP2 data in this field.Comment: Accepted for publication in AP
AEGIS: Infrared Spectroscopy of An Infrared Luminous Lyman Break Galaxy at z=3.01
We report the detection of rest--frame 6.2 and 7.7 \micron emission features
arising from Polycyclic Aromatic Hydrocarbons (PAH) in the Spitzer/IRS spectrum
of an infrared-luminous Lyman break galaxy at z=3.01. This is currently the
highest redshift galaxy where these PAH emission features have been detected.
The total infrared luminosity inferred from the MIPS 24 \micron and radio flux
density is 2 L, which qualifies this object as a
so--called hyperluminous infrared galaxy (HyLIRG). However, unlike local
HyLIRGs which are generally associated with QSO/AGNs and have weak or absent
PAH emission features, this HyLIRG has very strong 6.2 and 7.7 \micron PAH
emission. We argue that intense star formation dominates the infrared emission
of this source, although we cannot rule out the presence of a deeply obscured
AGN. This LBG appears to be a distorted system in the HST ACS F606W and F814W
images, possibly indicating that a significant merger or interaction is driving
the large IR luminosity
An Investigation of the Dust Content in the Galaxy pair NGC 1512/1510 from Near-Infrared to Millimeter Wavelengths
We combine new ASTE/AzTEC 1.1 mm maps of the galaxy pair NGC 1512/1510 with
archival Spitzer IRAC and MIPS images covering the wavelength range 3.6--160 um
from the SINGS project to derive accurate dust masses in each galaxy, and in
sub--galactic regions in NGC 1512. The two galaxies form a pair consisting of a
large, high--metallicity spiral (NGC 1512) and a low metallicity, blue compact
dwarf (NGC 1510). The derived total dust masses are (2.4+/-0.6) 10^7 Msun and
(1.7+/-3.6) 10^5 Msun for NGC 1512 and NGC 1510, respectively. The derived
ratio of dust mass to H I gas mass for the galaxy pair (0.0034) is much lower
than expected, while regions within NGC 1512, specifically the central region
and the arms, do not show such unusually low ratios; furthermore, the
dust--to--gas ratio is within expectations for NGC 1510. These results suggest
that a fraction of the H I included in the determination of the M_d/M_HI ratio
of the NGC 1512/1510 pair is not associated with the star forming disks/regions
of either galaxy. We also perform simple two--temperature (warm + cold)
modified--blackbody fits to the far--infrared/mm data. The warm dust
temperature of the low--metallicity NGC 1510 (~36 K) is substantially higher
than that of the high--metallicity NGC 1512 (~24 K). In both galaxies, a
substantial fraction (>93%) of the total dust mass is in a cool dust component,
with temperatures 14--16 K for NGC 1512 and 15--24 K for NGC 1510. In contrast,
the warm dust in the arms and central regions of NGC 1512 represents a much
larger fraction of the total dust content, in agreement with the fact that all
three regions have higher specific star formation rates than the average in the
galaxy.Comment: 33 pages, 4 figures, 4 tables, accepted for publication in A
Abell 3560, a galaxy cluster at the edge of a major merging event
In this paper we study A3560, a rich cluster at the southern periphery of the
A3558 complex, a chain of interacting clusters in the central part of the
Shapley Concentration supercluster.
From a ROSAT-PSPC map we find that the X-ray surface brightness distribution
of A3560 is well described by two components, an elliptical King law and a more
peaked and fainter structure, which has been modeled with a Gaussian. The main
component, corresponding to the cluster, is elongated with the major axis
pointing toward the A3558 complex. The second component, centered on the
Dumb-bell galaxy which dominates the cluster, appears significantly offset (by
about 0.15 Mpc) from the cluster X-ray centroid.
From a Beppo-SAX observation we derive the radial temperature profile,
finding that the temperature is constant (at kT~3.7 keV) up to 8 arcmin,
corresponding to 0.3 Mpc: for larger distances, the temperature significantly
drops to kT~1.7 keV. We analyze also temperature maps, dividing the cluster in
4 sectors and deriving the temperature profiles in each sector: we find that
the temperature drop is more sudden in the sectors which point towards the
A3558 complex.
From VLA radio data, at 20 and 6 cm, we find a peculiar bright extended radio
source (J1332-3308), composed by a core (centered on the northern component of
the Dumb-bell galaxy), two lobes, a "filament" and a diffuse component. The
morphology of the source could be interpreted either with a strong interaction
of the radio source with the intracluster medium or with the model of
intermittency of the central engine.Comment: 8 pages with encapsulated figures, A&A in pres
Radio continuum and far-infrared emission from the galaxies in the Eridanus group
The Eridanus galaxies follow the well-known radio-FIR correlation. Majority
(70%) of these galaxies have their star formation rates below that of the Milky
Way. The galaxies having a significant excess of radio emission are identified
as low luminosity AGNs based on their radio morphologies obtained from the GMRT
observations. There are no powerful AGNs (L{20cm} > 10^{23} W Hz^{-1}) in the
group. The two most far-infrared and radio luminous galaxies in the group have
optical and HI morphologies suggestive of recent tidal interactions. The
Eridanus group also has two far-infrared luminous but radio-deficient galaxies.
It is believed that these galaxies are observed within a few Myr of the onset
of an intense star formation episode after being quiescent for at least a 100
Myr. The upper end of the radio luminosity distribution of the Eridanus
galaxies (L_{20cm} ~ 10^{22} W Hz^{-1}) is consistent with that of the field
galaxies, other groups, and late-type galaxies in nearby clusters.Comment: 16 pages; Accepted for publication in Journal of Astroph. & Astron.
March, 200
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