269 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
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
Number Counts of Bright Extremely Red Objects: Evolved Massive Galaxies at z~1
We present results on number counts of Extremely Red Objects (EROs) in a 2850
arcmin^2 near-infrared survey performed in European Large Area ISO Survey
(ELAIS) fields at K<17.5. Counts of EROs are extended to brighter levels than
available previously, giving 0.002 +/- 0.001 arcmin^-2 at K<16.5 and consistent
numbers with literature values at fainter magnitudes. Photometric redshifts
from HYPERZ as well as GRASIL model SEDs of galaxies imply that our EROs are
located in the range z=0.7-1.5, with the bulk of the population at z~1. Taking
advantage of the ISO data in the fields, we use mid-IR detections to constrain
the number of dusty EROs, and also discuss the superior capabilities of Spitzer
Space Telescope to detect dusty EROs. Both the mid-IR data and the use of
colour-colour diagrammes indicate that at most 10-20% of the EROs in this
bright regime are dusty starbursting systems. The space density of our EROs,
interpreted to be counterparts of local >2-3L^star massive galaxies at around
z~1, is estimated to be approx. 2x10^-5 Mpc^-3, which is consistent with local
values. Furthermore, the cumulative number counts at our bright magnitudes are
remarkably well fitted by pure luminosity evolution models.Comment: A&A, accepted, 14 pages and 8 ps-fig
The Canada-UK Deep Submillimeter Survey VI: The 3-Hour Field
We present the complete submillimeter data for the Canada-UK Deep
Submillimeter Survey (CUDSS) 3-hour field. The obeservations were taken with
the Submillimeter Common-User Bolometer Array (SCUBA) on the James Clerk
Maxwell Telescope on Mauna Kea. The 3-hour field is one of two main fields in
our survey and covers 60 square arcminutes to a 3-sigma depth of 3 mJy. In this
field we have detected 27 sources above 3-sigma and 15 above 3.5-sigma. We
assume the source counts follow the form and
measure = 3.3. This is in good agreement with previous
studies and further supports our claim (Eales et al., 2000) that SCUBA sources
brighter than 3 mJy produce ~20% of the 850m background energy. Using
preliminary ISO 15 m maps and VLA 1.4 GHz data we have identified
counterparts for six objects and have marginal detections at 450m for two
additional sources. With this information we estimate a median redshift for the
sample of 2.00.5, with 10% lying at 1. We have measured the
angular clustering of S850 > 3 mJy sources using the source catalogues from the
CUDSS two main fields, the 3-hour and 14-hour fields, and find a marginal
detection of clustering, primarily from the 14-hour field, of
. This is consistent with clustering at
least as strong as that seen for the Lyman-break galaxy population and the
Extremely Red Objects. Since SCUBA sources are selected over a broader range in
redshifts than these two populations the strength of the true spatial
clustering is expected to be correspondingly stronger.Comment: 17 pages, 8 figures, submitted to Ap
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