323 research outputs found
The Disks of Galaxies with Seyfert and Starburst Nuclei: II. Near-Infrared Structural Properties
We have derived the near-infrared structural components of a sample of
Seyfert and starburst (SBN) host galaxies by fitting the images of Hunt et al.
(1997,ApJS,108,229) with a new two-dimensional decomposition algorithm. An
analysis of the fitted parameters shows that Seyfert 1 and SBN bulges resemble
normal early-type bulges in structure and color, with (J-K)^c_b about 0.1 mag
redder than disk (J-K)^c_d. Seyfert 2 bulges, instead, are bluer than normal
with (J-K)^c_b ~ (J-K)^c_d. Seyfert disks (especially Type 1), but not those of
SBNs, are abnormally bright (in surface brightness), significantly more so than
even the brightest normal disks. Seyfert disks are also compact, but similar to
those in normal early-type spirals. For a given mass, Seyferts and especially
SBNs are abnormally rich in neutral hydrogen, and there is strong, albeit
indirect, evidence for lower mass-to-light (M/L) ratios in Seyfert and SBN
disks, but for normal M/Ls in their bulges. In Seyferts and SBNs, HI mass
fractions and M/L ratios are anticorrelated, and we attribute the high gas mass
fractions and low M/Ls in SBNs and several Seyferts to ongoing star formation.
Such abundant gas in Seyferts would be expected to inhibit bar formation, which
may explain why active galaxies are not always barred.Comment: 25 pgs (two-column, single-spaced) including 8 incorporated figures
and 2 tables (aas2pp4, amssym, epsfig). Accepted for publication in Ap
The Inner Scale Length of Spiral Galaxy Rotation Curves
We use the tapering effect of Halpha/[NII] rotation curves of spiral galaxies
first noted by Goad & Roberts (1981) to investigate the internal extinction in
disks. The scale length of exponential fits to the inner part of rotation
curves depends strongly on the disk axial ratio. Preliminary modelling of the
effect implies substantial opacity of the central parts of disks at a
wavelength of 0.66 \mu. In addition, the average kinematic scale length of
rotation curves, when corrected to face--on perspective, has a nearly constant
value of about 1.7 h^{-1} kpc, for all luminosity classes. The interpretation
of that effect, as the result of the increasing dominance of the baryonic mass
in the inner parts of galaxies, yields a mean baryonic mass--to--light ratio in
the I band \Upsilon_I= 2.7h M_sun/L_{sun,I}, within the inner 1.7 h^{-1} kpc of
disks.Comment: 11 pages, including one table and one figure, AAStex scheduled to
appear in the Astrophysical Journal (Letters
The Clustering of Extragalactic Extremely Red Objects
We have measured the angular and spatial clustering of 671 K5
Extremely Red Objects (EROs) from a 0.98 square degree sub-region of the NOAO
Deep Wide-Field Survey (NDWFS). Our study covers nearly 5 times the area and
has twice the sample size of any previous ERO clustering study. The wide field
of view and BwRIK passbands of the NDWFS allow us to place improved constraints
on the clustering of z=1 EROs. We find the angular clustering of EROs is
slightly weaker than in previous measurements, and w(1')=0.25+/-0.05 for
K<18.40 EROs. We find no significant correlation of ERO spatial clustering with
redshift, apparent color or absolute magnitude, although given the
uncertainties, such correlations remain plausible. We find the spatial
clustering of K5 EROs is well approximated by a power-law, with
r_0=9.7+/-1.1 Mpc/h in comoving coordinates. This is comparable to the
clustering of 4L* early-type galaxies at z<1, and is consistent with the
brightest EROs being the progenitors of the most massive ellipticals. There is
evidence of the angular clustering of EROs decreasing with increasing apparent
magnitude, when NDWFS measurements of ERO clustering are combined with those
from the literature. Unless the redshift distribution of K>20 EROs is very
broad, the spatial clustering of EROs decreases from r_0=9.7+/-1.1 Mpc/h for
K20 EROs.Comment: Accepted for publication in the ApJ. 29 pages with 10 figures. The
NOAO Deep Wide-Field Survey Bootes data release is available online at
http://www.noao.edu/noao/noaodeep
The Evolution of Dust Opacity in Galaxies
(Abridged) We investigate the evolution of the opacity of galaxies as a
function of redshift, using simple assumptions about the metal and dust
enrichment of the gas and the distribution of dust in galaxies. We use an
iterative procedure to reconstruct the intrinsic Star Formation Rate (SFR)
density of galaxies with redshift, by applying dust obscuration corrections to
the observed UV emission. The iterative procedure converges to multiple
solutions for the intrinsic SFR density, divided into two basic classes. The
first class of solutions predicts relatively large UV attenuation at high
redshift, with A(1500 A)=1.9 mag at z~3, and smaller attenuations at z<1, with
A(2800 A)=1.25 mag. The SFR density of this set of solutions is constant for
z>~1.2 and declines for z<1.2; it resembles in shape the ``monolithic
collapse'' scenario for star formation. The second class of solutions predicts
relatively low UV attenuations at high redshift, with A(1500 A)=0.75 mag at
z~3, and larger attenuations at z<1, with A(2800 A)=1.50 mag. The SFR density
in this case has a peak at z~1.2. The advantages and shortcomings of both
classes are analyzed in the light of available observational constraints,
including the opacity of galaxies at 0<z<1 and the intensity and spectral
energy distribution of the cosmic infrared background from the COBE DIRBE and
FIRAS data. We conclude that both classes of models are acceptable within the
current uncertainties, but the ``monolithic collapse'' class matches the
available observations better than the other one. We also investigate the
dependence of our solutions on the different model assumptions.Comment: 54 pages, includes 1 embedded postscript Table and 22 embedded
postscript Figures, Latex, uses AAS Latex macro. Accepted for publication in
the Astrophysical Journa
Internal Extinction in Spiral Galaxies in the Near Infrared
In order to study the effects of internal extinction in spiral galaxies we
search for correlations of near infrared (NIR) photometric parameters with
inclination. We use data from the 2 Micron All-Sky Survey (2MASS) Extended
Source Catalog (XSC) on 15,224 spiral galaxies for which we also have
redshifts. For 3035 of the galaxies, I-band photometry is available which is
included in the analysis. From the simple dependence of reddening on
inclination we derive a lower limit to the difference in magnitude between the
face-on and edge-on aspect of 0.9, 0.3 and 0.1 magnitudes in I (0.81 um), J
(1.25 um) and H (1.65 um) bands. We find that the faintest isophotal radius
reported in the XSC (at the 21st mag/arc sq level) is closer to the centers of
the galaxies than other common isophotal measures (e.g. the 23.5 mag/arc sq
radius in I-band), and argue that it should not be assumed to represent an
outer isophote at which galaxies are transparent at all viewing angles. A
simple linear extinction law (i.e. Delta M = gamma log(a/b)) is not adequate
for the full range of disk inclinations and we adopt both a bi-linear and a
quadratic law. A simple photometric model is used to explain the observed
behavior. Internal extinction depends on galaxy luminosity. We show that for
galaxies with a K total magnitude dimmer than -20, -20.7 and -20.9 the data
indicates zero extinction in J, H and K respectively, while disk opacity
increases monotonically with increasing disk luminosity.Comment: Accepted for publication in AJ (July 2003). 28 pages, 13 figures.
Revised version corrects some typos including an error in the reported
luminosity dependence of the extinction correctio
Molecular Gas in the Lensed Lyman Break Galaxy cB58
We have used the IRAM Plateau de Bure Interferometer to map CO(3-2) emission
from the gravitationally lensed Lyman break galaxy MS1512-cB58. This is the
first detection of a molecular emission line in any Lyman break system; its
integrated intensity implies a total molecular gas mass of 6.6e9 Msun, while
its width implies a dynamical mass of 1.0e10 csc^2i Msun (for a flat Lambda=0.7
cosmology). These estimates are in excellent concordance with nearly all
parameters of the system measured at other wavelengths, and yield a consistent
picture of past and future star formation with no obvious discrepancies
requiring explanation by differential lensing. In particular, we find that the
age and remaining lifetime of the current episode of star formation are likely
to be similar; the surface densities of star formation and molecular gas mass
are related by a Schmidt law; and the fraction of baryonic mass already
converted into stars is sufficient to account for the observed enrichment of
the interstellar medium to 0.4 Zsun. Barring substantial gas inflow or a major
merger, the stars forming in the current episode will have mass and coevality
at z=0 similar to those of a spiral bulge. Assuming cB58 is a typical Lyman
break galaxy apart from its magnification, its global parameters suggest that
the prescriptions for star formation used in some semi-analytic models of
galaxy evolution require moderate revision, although the general prediction
that gas mass fraction should increase with redshift is validated. [abridged]Comment: 41 pages, 6 figures, accepted by Ap
The Radio/Optical Catalog of the SSA13 Field
We present a 1.4-GHz catalog of 810 radio sources (560 sources in the
complete sample) with 1.8" resolution found within a 17' radius in the SSA13
field (RA=13h12m,DEC=42d38'). The radio image from the VLA has an rms noise
level of 4.82 microJy/beam at the field center, and Subaru optical images in
r-band (6300A) and z-band (9200A) have a three-sigma detection magnitude of
26.1 and 24.9, respectively. 88% of the radio sources are identified with an
optical counterpart, and there is significantly more reddening for objects
fainter than 24-mag. The radio and optical parameters are tabulated, and source
morphologies are displayed by radio contours overlaying optical false-color
images. The radio structures show a wealth of complexity and these are
classified into a small number of categories. About one-third of the radio
sources are larger than 1.2" and their orientation is often similar to that of
the associated galaxy or binary-galaxy system. The density of sources in the
SSA13 field above 75 microJy is 0.40 per square arcmin, with a slope of -2.43
in the differential counts. The radio spectral index may steepen for sources
below 75 microJy. We estimate that at most 40% of the microJansky radio sources
are dominated by AGN processes.Comment: 50 pages, 14 figures of which fig 6 contains 33 parts. In press,
Astrophysical Journal, Supp
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