243 research outputs found
WSRT observations and surface photometry of two unusual spiral galaxies
We discuss the results of a mass decomposition of two spiral galaxies, NGC
6824 and UGC 11919. In a previous analysis of the Hyperleda catalog, the
galaxies were identified as having a peculiar dynamical . The aim of this
study is to confirm or disprove the preliminary findings, indicating a
non-standard stellar initial mass function (IMF) for the galaxies. The surface
photometry in B, V, and R bands was carried out with the Apache Point 0.5-m
telescope and the \ion{H}{I} data cubes were obtained with the Westerbork
Synthesis Radio Telescope (WSRT). Photometric profiles were decomposed into
bulge and exponential disk components. Using the obtained \ion{H}{I} data
cubes, rotation curves of both galaxies were constructed. Employing the
photometric profiles, the mass distribution of the galaxies was decomposed into
mass components: bulge, stellar disk, gas, and pseudo-isothermal dark halo. We
conclude that NGC 6824 possesses a stellar disk with mass-to-light ratio
, in agreement with its color . On the
contrary, UGC 11919 appears to have a very lightweight disk. Its dynamically
estimated mass corresponds to a low stellar disk mass-to-light ratio
. Under standard assumptions, this ratio does
not agree with the relatively red color of the disk, while a bottom light
stellar initial mass function is needed to explain the observations.Comment: 14 pages, 14 figures, accepted for publication in Astronomy and
Astrophysic
The stellar disk thickness of LSB galaxies
We present surface photometry results for a sample of eleven edge-on galaxies
observed with the 6m telescope at the Special Astrophysical Observatory
(Russia). The photometric scale length, scale height, and central surface
brightness of the stellar disks of our sample galaxies are estimated. We show
that four galaxies in our sample, which are visually referred as objects of the
lowest surface brightness class in the Revised Flat Galaxies Catalog, have bona
fide low surface brightness (LSB) disks. We find from the comparison of
photometric scales that the stellar disks of LSB galaxies are thinner than
those of high surface brightness (HSB) ones. There is a clear correlation
between the central surface brightness of the stellar disk and its vertical to
radial scale ratio. The masses of spherical subsystems (dark halo + bulge) and
the dark halo masses are obtained for the sample galaxies based on the
thickness of their stellar disks. The LSB galaxies tend to harbor more massive
spherical subsystems than the HSB objects, whereas no systematic difference in
the dark halo masses between LSB and HSB galaxies is found. At the same time,
the inferred mass-to-luminosity ratio for the LSB disks appears to be
systematically higher than for HSB disks.Comment: 33 pages with 17 Postscript figures, uses aastex.cls, accepted by Ap
Relation Between the Thickness of Stellar Disks and the Relative Mass of Dark Halo in Galaxies
We consider a thickness of stellar disks of late-type galaxies by analyzing
the R and K_s band photometric profiles for two independent samples of edge-on
galaxies. The main goal is to verify a hypotesis that a thickness of old
stellar disks is related to the relative masses of the spherical and disk
components of galaxies. We confirm that the radial-to-vertical scale length
ratio for galactic disks increases (the disks become thinner) with the
increasing of total mass-to-light ratio of the galaxies, which characterize the
contribution of dark halo to the total mass, and with the decreasing of central
deprojected disk brightness (surface density). Our results are in good
agreement with numerical models of collisionless disks evolved from subcritical
velocity dispersion state to a marginally stable equilibrium state. This
suggests that in most galaxies the vertical stellar velocity dispersion, which
determine the equilibrium disk thickness, is close to the minimum value, that
ensures disk stability. The thinnest edge-on disks appear to be low brightness
galaxies (after deprojection) in which a dark halo mass far exceeds a mass of
the stellar disk.Comment: 13 pages. To be Published in Astronomy Letters, v.28(2002
SDSS-IV MANGA: Spatially Resolved Star Formation Main Sequence and LI(N)ER Sequence
We present our study on the spatially resolved H_alpha and M_star relation
for 536 star-forming and 424 quiescent galaxies taken from the MaNGA survey. We
show that the star formation rate surface density (Sigma_SFR), derived based on
the H_alpha emissions, is strongly correlated with the M_star surface density
(Sigma_star) on kpc scales for star- forming galaxies and can be directly
connected to the global star-forming sequence. This suggests that the global
main sequence may be a consequence of a more fundamental relation on small
scales. On the other hand, our result suggests that about 20% of quiescent
galaxies in our sample still have star formation activities in the outer region
with lower SSFR than typical star-forming galaxies. Meanwhile, we also find a
tight correlation between Sigma_H_alpha and Sigma_star for LI(N)ER regions,
named the resolved "LI(N)ER" sequence, in quiescent galaxies, which is
consistent with the scenario that LI(N)ER emissions are primarily powered by
the hot, evolved stars as suggested in the literature.Comment: 6 pages, 4 figures. ApJ Letter accepte
The clustering of intermediate redshift quasars as measured by the Baryon Oscillation Spectroscopic Survey
We measure the quasar two-point correlation function over the redshift range
2.2<z<2.8 using data from the Baryon Oscillation Spectroscopic Survey. We use a
homogeneous subset of the data consisting of 27,129 quasars with spectroscopic
redshifts---by far the largest such sample used for clustering measurements at
these redshifts to date. The sample covers 3,600 square degrees, corresponding
to a comoving volume of 9.7(Gpc/h)^3 assuming a fiducial LambdaCDM cosmology,
and it has a median absolute i-band magnitude of -26, k-corrected to z=2. After
accounting for redshift errors we find that the redshift space correlation
function is fit well by a power-law of slope -2 and amplitude s_0=(9.7\pm
0.5)Mpc/h over the range 3<s<25Mpc/h. The projected correlation function, which
integrates out the effects of peculiar velocities and redshift errors, is fit
well by a power-law of slope -1 and r_0=(8.4\pm 0.6)Mpc/h over the range
4<R<16Mpc/h. There is no evidence for strong luminosity or redshift dependence
to the clustering amplitude, in part because of the limited dynamic range in
our sample. Our results are consistent with, but more precise than, previous
measurements at similar redshifts. Our measurement of the quasar clustering
amplitude implies a bias factor of b~3.5 for our quasar sample. We compare the
data to models to constrain the manner in which quasars occupy dark matter
halos at z~2.4 and infer that such quasars inhabit halos with a characteristic
mass of ~10^{12}Msun/h with a duty cycle for the quasar activity of 1 per
cent.Comment: 20 pages, 18 figures. Minor modifications to match version accepted
by journa
Galactic Globular and Open Clusters in the Sloan Digital Sky Survey. I. Crowded Field Photometry and Cluster Fiducial Sequences in ugriz
We present photometry for globular and open cluster stars observed with the
Sloan Digital Sky Survey (SDSS). In order to exploit over 100 million stellar
objects with r < 22.5 mag observed by SDSS, we need to understand the
characteristics of stars in the SDSS ugriz filters. While star clusters provide
important calibration samples for stellar colors, the regions close to globular
clusters, where the fraction of field stars is smallest, are too crowded for
the standard SDSS photometric pipeline to process. To complement the SDSS
imaging survey, we reduce the SDSS imaging data for crowded cluster fields
using the DAOPHOT/ALLFRAME suite of programs and present photometry for 17
globular clusters and 3 open clusters in a SDSS value-added catalog. Our
photometry and cluster fiducial sequences are on the native SDSS 2.5-meter
ugriz photometric system, and the fiducial sequences can be directly applied to
the SDSS photometry without relying upon any transformations. Model photometry
for red giant branch and main-sequence stars obtained by Girardi et al. cannot
be matched simultaneously to fiducial sequences; their colors differ by
~0.02-0.05 mag. Good agreement (< ~0.02 mag in colors) is found with Clem et
al. empirical fiducial sequences in u'g'r'i'z' when using the transformation
equations in Tucker et al.Comment: 30 pages, 25 figures. Accepted for publication in ApJS. Version with
high resolution figures available at
http://www.astronomy.ohio-state.edu/~deokkeun/AnJohnson.pd
Photometric deprojection of edge-on galaxies
Photometric deprojection is used to determine the stellardisk and bulge
parameters for several edgeon galaxies from the FGC catalog. The assumption
that the galaxies of our sample belonging to the fourth (i.e., lowest)
surfacebrightness class in the FGC are edgeon, lowsurfacebrightness (LSB)
galaxies is considered.Comment: 6 pages including 3 figures. Have been published in Astronomy
Letters, v.26, p.219, 2000 (Translated from Pis'ma v Astronomicheskiy
Zhurnal, V.26, N.4, 2000, p.266.
The Gas Content in Galactic Disks: Correlation with Kinematics
We consider the relationship between the total HI mass in late-type galaxies
and the kinematic properties of their disks. The mass for galaxies with
a wide variety of properties, from dwarf dIrr galaxies with active star
formation to giant low-brightness galaxies, is shown to correlate with the
product ( is the rotational velocity, and is the radial
photometric disks scale length), which characterizes the specific angular
momentum of the disk. This relationship, along with the anticorrelation between
the relative mass of HI in a galaxy and , can be explained in terms of the
previously made assumption that the gas density in the disks of most galaxies
is maintained at a level close to the threshold (marginal) stability of a
gaseous layer to local gravitational perturbations. In this case, the
regulation mechanism of the star formation rate associated with the growth of
local gravitational instability in the gaseous layer must play a crucial role
in the evolution of the gas content in the galactic disk.Comment: revised version to appear in Astronomy Letters, 8 pages, 5 EPS
figure
Characterization of low-mass companions to objects of interest observed with APOGEE-N
We report the characterization of 28 low-mass
() companions
to objects of interest (KOIs), eight of which were previously
designated confirmed planets. These objects were detected as transiting
companions to Sun-like stars (G and F dwarfs) by the mission
and are confirmed as single-lined spectroscopic binaries in the current work
using the northern multiplexed Apache Point Observatory Galactic Evolution
Experiment near-infrared spectrograph (APOGEE-N) as part of the third and
fourth Sloan Digital Sky Surveys. We have observed hundreds of KOIs using
APOGEE-N and collected a total of 43,175 spectra with a median of 19 visits and
a median baseline of years per target. We jointly model the
photometry and APOGEE-N radial velocities to derive
fundamental parameters for this subset of 28 transiting companions. The radii
for most of these low-mass companions are over-inflated (by ) when
compared to theoretical models. Tidally locked M dwarfs on short period orbits
show the largest amount of inflation, but inflation is also evident for
companions that are well separated from the host star. We demonstrate that
APOGEE-N data provides reliable radial velocities when compared to precise
high-resolution spectrographs that enable detailed characterization of
individual systems and the inference of orbital elements for faint ()
KOIs. The data from the entire APOGEE-KOI program is public and presents an
opportunity to characterize an extensive subset of the binary population
observed by .Comment: 98 pages (include 56 for the figure sets), 10 tables, 7 figures, 2
figure sets, accepted for publication in ApJ
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