258 research outputs found
Radial distribution of stars, gas and dust in SINGS galaxies. III. Modeling the evolution of the stellar component in galaxy disks
(Abridged) We analyze the evolution of 42 spiral galaxies in the Spitzer
Infrared Nearby Galaxies Survey, using extinction-corrected UV, optical and
near-infrared radial profiles to probe the emission of stars of different ages
as a function of radius. We fit these profiles with models that describe the
chemical and spectro-photometric evolution of spiral disks within a
self-consistent framework. These backward models succesfully reproduce the
multi-wavelength profiles of our galaxies, except the UV profiles of some
early-type disks. From the model fitting we infer the maximum circular velocity
of the rotation curve (Vc) and the dimensionless spin parameter (lambda). The
values of Vc are in good agreement with the velocities measured in HI rotation
curves. While our sample is not volume-limited, the resulting distribution of
spins is close to the lognormal function obtained in cosmological N-body
simulations, peaking at ~0.03 regardless of the total halo mass. We do not find
any evident trend between spin and Hubble type, besides an increase in the
scatter for the latest types. According to the model, galaxies evolve along a
roughly constant mass-size relation, increasing their scale-lengths as they
become more massive. The radial scale-length of most disks in our sample seems
to have increased at a rate of 0.05-0.06 kpc/Gyr, being now 20-25% larger than
at z=1.Comment: Accepted for publication in ApJ. 32 pages in emulateapj format, 25
figures. The whole figureset of Fig. 2 can be downloaded from
http://www.cv.nrao.edu/~jmunoz/f2_all.p
On the semiclassical mass of -kinks
One-loop mass shifts to the classical masses of stable kinks arising in a
massive non-linear -sigma model are computed. Ultraviolet
divergences are controlled using the heat kernel/zeta function regularization
method. A comparison between the results achieved from exact and
high-temperature asymptotic heat traces is analyzed in depth.Comment: RevTex file, 15 pages, 2 figures. Version to appear in Journal of
Physics
Radial distribution of stars, gas and dust in SINGS galaxies. I. Surface photometry and morphology
We present ultraviolet through far-infrared surface brightness profiles for
the 75 galaxies in the Spitzer Infrared Nearby Galaxies Survey (SINGS). The
imagery used to measure the profiles includes GALEX UV data, optical images
from KPNO, CTIO and SDSS, near-IR data from 2MASS, and mid- and far-infrared
images from Spitzer. Along with the radial profiles, we also provide
multi-wavelength asymptotic magnitudes and several non-parametric indicators of
galaxy morphology: the concentration index (C_42), the asymmetry (A), the Gini
coefficient (G) and the normalized second-order moment of the brightest 20% of
the galaxy's flux (M_20). Our radial profiles show a wide range of morphologies
and multiple components (bulges, exponential disks, inner and outer disk
truncations, etc.) that vary not only from galaxy to galaxy but also with
wavelength for a given object. In the optical and near-IR, the SINGS galaxies
occupy the same regions in the C_42-A-G-M_20 parameter space as other normal
galaxies in previous studies. However, they appear much less centrally
concentrated, more asymmetric and with larger values of G when viewed in the UV
(due to star-forming clumps scattered across the disk) and in the mid-IR (due
to the emission of Polycyclic Aromatic Hydrocarbons at 8.0 microns and very hot
dust at 24 microns).Comment: 66 pages in preprint format, 14 figures, published in ApJ. The
definitive publisher authenticated version is available online at
http://dx.doi.org/10.1088/0004-637X/703/2/156
A systematic cross-search for radio/infrared counterparts of XMM-Newton sources
We present a catalog of cross-correlated radio, infrared and X-ray sources
using a very restrictive selection criteria with an IDL-based code developed by
us. The significance of the observed coincidences was evaluated through Monte
Carlo simulations of synthetic sources following a well-tested protocol. We
found 3320 coincident radio/X-ray sources with a high statistical significance
characterized by the sum of error-weighted coordinate differences. For 997 of
them, 2MASS counterparts were found. The percentage of chance coincidences is
less than 1%. X-ray hardness ratios of well-known populations of objects were
used to provide a crude representation of their X-ray spectrum and to make a
preliminary diagnosis of the possible nature of unidentified X-ray sources. The
results support the fact that the X-ray sky is largely dominated by Active
Galactic Nuclei at high galactic latitudes (|b| >= 10^\circ). At low galactic
latitudes (|b| <= 10^\circ) most of unidentified X-ray sources (~94%) lie at
|b| <= 2^\circ. This result suggests that most of the unidentified sources
found toward the Milky Way plane are galactic objects. Well-known and
unidentified sources were classified in different tables with their
corresponding radio/infrared and X-ray properties. These tables are intended as
a useful tool for researchers interested in particular identifications.Comment: Accepted for publication in Ap&SS. 47 pages, 10 figures. On-line
material: figures and table
Star formation in the extended gaseous disk of the isolated galaxy CIG 96
We study the Kennicutt-Schmidt star formation law and efficiency in the
gaseous disk of the isolated galaxy CIG 96 (NGC 864), with special emphasis on
its unusually large atomic gas (HI) disk (r_HI/r_25 = 3.5, r_25 = 1.'85). We
present deep GALEX near and far ultraviolet observations, used as a recent star
formation tracer, and we compare them with new, high resolution (16", or 1.6
kpc) VLA HI observations. The UV and HI maps show good spatial correlation
outside the inner 1', where the HI phase dominates over H_2. Star-forming
regions in the extended gaseous disk are mainly located along the enhanced HI
emission within two (relatively) symmetric giant gaseous spiral arm-like
features, which emulate a HI pseudo-ring at a r \simeq 3' . Inside such
structure, two smaller gaseous spiral arms extend from the NE and SW of the
optical disk and connect to the previously mentioned HI pseudo-ring.
Interestingly, we find that the (atomic) Kennicutt-Schmidt power law index
systematically decreases with radius, from N \simeq 3.0 +- 0.3 in the inner
disk (0.'8 - 1.'7) to N = 1.6 +- 0.5 in the outskirts of the gaseous disk (3.'3
- 4.'2). Although the star formation efficiency (SFE), the star formation rate
per unit of gas, decreases with radius where the HI component dominates as is
common in galaxies, we find that there is a break of the correlation at r = 1.5
r_25. At radii 1.5 r_25 < r < 3.5 r_25, mostly within the HI pseudo-ring
structure, there exist regions whose SFE remains nearly constant, SFE \simeq
10^-11 yr^-1. We discuss about possible mechanisms that might be triggering the
star formation in the outskirts of this galaxy, and we suggest that the
constant SFE for such large radii r > 2 r_25 and at such low surface densities
might be a common characteristic in extended UV disk galaxies.Comment: 12 pages, 7 figures, 1 table. Accepted for publication in Ap
Integral Field Spectroscopy and multi-wavelength imaging of the nearby spiral galaxy NGC5668: an unusual flattening in metallicity gradient
We present the analysis of the full bi-dimensional optical spectral cube of
the nearby spiral galaxy NGC 5668, observed with the PPAK IFU at the Calar Alto
observatory 3.5m telescope. We make use of broad-band imaging to provide
further constraints on the evolutionary history of the galaxy. This dataset
will allow us to improve our understanding of the mechanisms that drive the
evolution of disks. We investigated the properties of 62 H II regions and
concentric rings in NGC 5668 and derived maps in ionized-gas attenuation and
chemical (oxygen) abundances. We find that, while inwards of
r\,\,4.4kpc\,\,0.36\, the derived
O/H ratio follows the radial gradient typical of spiral galaxies, the abundance
gradient beyond r flattens out. The analysis of the multi-wavelength
surface brightness profiles of NGC 5668 is performed by fitting these profiles
with those predicted by chemo-spectrophotometric evolutionary models of galaxy
disks. From this, we infer a spin and circular velocity of =0.053 and
v=167\,km\,s, respectively. The metallicity gradient and rotation
curve predicted by this best-fitting galaxy model nicely match the values
derived from the IFU observations, especially within r\,\sim36\arcsec. The
same is true for the colors despite of some small offsets and a reddening in
the bluest colors beyond that radius. On the other hand, deviations of some of
these properties in the outer disk indicate that a secondary mechanism,
possibly gas transfer induced by the presence of a young bar, must have played
a role in shaping the recent chemical and star formation histories of NGC 5668.Comment: 44 pages, 13 figures, Accepted for publication in ApJ. arXiv admin
note: text overlap with arXiv:astro-ph/020649
The Thick Disk in the Galaxy NGC 4244 from S^4G Imaging
If thick disks are ubiquitous and a natural product of disk galaxy formation and/or evolution processes, all
undisturbed galaxies that have evolved during a significant fraction of a Hubble time should have a thick disk. The
late-type spiral galaxy NGC 4244 has been reported as the only nearby edge-on galaxy without a confirmed thick
disk. Using data from the Spitzer Survey of Stellar Structure in Galaxies (S^4G) we have identified signs of two disk
components in this galaxy. The asymmetries between the light profiles on both sides of the mid-plane of NGC 4244
can be explained by a combination of the galaxy not being perfectly edge-on and a certain degree of opacity of
the thin disk. We argue that the subtlety of the thick disk is a consequence of either a limited secular evolution in
NGC 4244, a small fraction of stellar material in the fragments which built the galaxy, or a high amount of gaseous
accretion after the formation of the galaxy
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