20 research outputs found
Mariner 9 high-resolution albedo mapping of Mars
Large and small scale albedo markings obtained from Mariner 9 photographs and ground based telescope observations are shown on quadrangle charts with a scale of 1:5,000,000. Mercator and stereographic projections at the same scale are presented of the various regions of Mars along with explanatory information about their preparation. Changes in the albedo for the Solis Lacus area were observed and are compared with previous data for the same region. Large scale relief maps covering up to 1.7 million sq miles of the Martian surface are included
Extinction in Star-Forming Disk Galaxies from Inclination-Dependent Composite Spectra
Extinction in galaxies affects their observed properties. In scenarios
describing the distribution of dust and stars in individual disk galaxies, the
amplitude of the extinction can be modulated by the inclination of the
galaxies. In this work we investigate the inclination dependency in composite
spectra of star-forming disk galaxies from the Sloan Digital Sky Survey Data
Release 5. In a volume-limited sample within a redshift range 0.065-0.075 and a
r-band Petrosian absolute magnitude range -19.5 to -22 which exhibits a flat
distribution of inclination, the inclined relative to face-on extinction in the
stellar continuum is found empirically to increase with inclination in the g,
r, and i bands. Within the central 0.5 intrinsic half-light radius of the
galaxies, the g-band relative extinction in the stellar continuum for the
highly-inclined objects (axis ratio b/a = 0.1) is 1.2 mag, agreeing with
previous studies. The extinction curve of the disk galaxies is given in the
restframe wavelengths 3700-8000 angstrom, identified with major optical
emission and absorption lines in diagnostics. The Balmer decrement remains
constant with inclination, suggesting a different kind of dust configuration
and/or reddening mechanism in the HII region from that in the stellar
continuum. One factor is shown to be the presence of spatially non-uniform
interstellar extinction, presumably caused by clumped dust in the vicinity of
the HII region.Comment: To appear in the Astrophysical Journa
Black Hole Mass, Host galaxy classification and AGN activity
We investigate the role of host galaxy classification and black hole mass in
a heterogeneous sample of 276 mostly nearby (z<0.1) X-ray and IR selected AGN.
Around 90% of Seyfert 1 AGN in bulge-dominated host galaxies (without disk
contamination) span a very narrow range in the observed 12um to 2-10keV
luminosity ratio (1<R_{IR/X}<7). This narrow dispersion incorporates all
possible variations among AGN central engines, including accretion mechanism
and efficiency, disk opening angle, orientation to sightline, covering fraction
of absorbing material, patchiness of X-ray corona and measured variability. As
a result, all models of X-ray and IR production in AGN are very strongly
constrained. Among Seyfert 1 AGN, median X-ray and IR luminosities increase
with black hole mass at >99% confidence. Using ring morphology of the host
galaxy as a proxy for lack of tidal interaction, we find that AGN luminosity in
host galaxies within 70Mpc is independent of host galaxy interaction for
Gyrs, suggesting that the timescale of AGN activity due to secular evolution is
much shorter than that due to tidal interactions. We find that LINER hosts have
lower 12um luminosity than the median 12um luminosity of normal disk- and
bulge-dominated galaxies which may represent observational evidence for past
epochs of feedback that supressed star formation in LINER host galaxies. We
propose that nuclear ULXs may account for the X-ray emission from LINER 2s
without flat-spectrum, compact radio cores. We confirmed the robustness of our
results in X-rays by comparing them with the 14-195keV 22-month BAT survey of
AGN, which is all-sky and unbiased by photoelectric absorption.Comment: MNRAS accepted. 14 pages, 11 figures, complete Table 1 in online
journa
Infrared composition of the Large Magellanic Cloud
The evolution of galaxies and the history of star formation in the Universe
are among the most important topics in today's astrophysics. Especially, the
role of small, irregular galaxies in the star-formation history of the Universe
is not yet clear. Using the data from the AKARI IRC survey of the Large
Magellanic Cloud at 3.2, 7, 11, 15, and 24 {\mu}m wavelengths, i.e., at the
mid- and near-infrared, we have constructed a multiwavelength catalog
containing data from a cross-correlation with a number of other databases at
different wavelengths. We present the separation of different classes of stars
in the LMC in color-color, and color-magnitude, diagrams, and analyze their
contribution to the total LMC flux, related to point sources at different
infrared wavelengths
The Calibration of Monochromatic Far-Infrared Star Formation Rate Indicators
(Abridged) Spitzer data at 24, 70, and 160 micron and ground-based H-alpha
images are analyzed for a sample of 189 nearby star-forming and starburst
galaxies to investigate whether reliable star formation rate (SFR) indicators
can be defined using the monochromatic infrared dust emission centered at 70
and 160 micron. We compare recently published recipes for SFR measures using
combinations of the 24 micron and observed H-alpha luminosities with those
using 24 micron luminosity alone. From these comparisons, we derive a reference
SFR indicator for use in our analysis. Linear correlations between SFR and the
70 and 160 micron luminosity are found for L(70)>=1.4x10^{42} erg/s and
L(160)>=2x10^{42} erg/s, corresponding to SFR>=0.1-0.3 M_sun/yr. Below those
two luminosity limits, the relation between SFR and 70 micron (160 micron)
luminosity is non-linear and SFR calibrations become problematic. The
dispersion of the data around the mean trend increases for increasing
wavelength, becoming about 25% (factor ~2) larger at 70 (160) micron than at 24
micron. The increasing dispersion is likely an effect of the increasing
contribution to the infrared emission of dust heated by stellar populations not
associated with the current star formation. The non-linear relation between SFR
and the 70 and 160 micron emission at faint galaxy luminosities suggests that
the increasing transparency of the interstellar medium, decreasing effective
dust temperature, and decreasing filling factor of star forming regions across
the galaxy become important factors for decreasing luminosity. The SFR
calibrations are provided for galaxies with oxygen abundance 12+Log(O/H)>8.1.
At lower metallicity the infrared luminosity no longer reliably traces the SFR
because galaxies are less dusty and more transparent.Comment: 69 pages, 19 figures, 2 tables; accepted for publication on Ap
Determining Star Formation Timescale and Pattern Speed in Nearby Spiral Galaxies
We present a revised method for simultaneous determination of the pattern
speed and star formation timescale of spiral galaxies, its application, and
results for CO and Ha images of nearby spiral galaxies. Out of 13 galaxies, we
were able to derive the 2 parameters for 5 galaxies. We categorize them as "C"
galaxies, and find (1) The corotation radius is close to the edge of the CO
data, and is about half of the optical radius for 3 galaxies. (2) The star
formation timescale is roughly consistent with the free-fall time of typical
molecular clouds, which indicates that the gravitational instability is the
dominant mechanism triggering star formation in spiral arms. (3) The timescale
is found to be almost independent of surface density of molecular gas,
metallicity, or spiral arm strengths. The number of "C" galaxies and the
quality of CO data, however, are not enough to confirm these relationships. We
also find that 2 other galaxies show no offsets between CO and Ha, although
their arms are clearly traced, and categorize them as "N" galaxies. The
presence of a bar could account for this feature, since these 2 galaxies are
both barred. With one galaxy excluded from our analysis due to its poor
rotation curve, offsets of the remaining 5 galaxies are found to be ambiguous.
We categorize them as "A" galaxies. The possible reasons for this ambiguity are
(1) the density wave is weaker, and/or (2) observational resolution and
sensitivity are not enough to detect the spiral arms and their offsets clearly.
The former is supported by our finding that the arm strengths of "A" galaxies
are slightly weaker than that of "C" galaxies. [abridged]Comment: 53 pages, 9 tables, 18 figures. Accepted to ApJ. Some figures are
downgraded. See http://www.astro.caltech.edu/~fegusa/ms_offset.pdf for
original versio
Uncovering multiple Wolf-Rayet star clusters and the ionized ISM in Mrk 178: the closest metal-poor Wolf-Rayet H ii galaxy
New integral field spectroscopy (IFS) has been obtained for the nearby metal-poor Wolf–Rayet (WR) galaxy Mrk 178 to examine the spatial correlation between its WR stars and the neighbouring ionized interstellar medium (ISM). The strength of the broad WR features and its low metallicity make Mrk 178 an intriguing object. We have detected the blue and red WR bumps in different locations across the field of view (∼300 pc × 230 pc) in Mrk 178. The study of the WR content has been extended, for the first time, beyond its brightest star-forming knot uncovering new WR star clusters. Using Large/Small Magellanic Cloud-template WR stars, we empirically estimate a minimum of ∼20 WR stars within the region sampled. Maps of the spatial distribution of the emission lines and of the physical–chemical properties of the ionized ISM have been created and analysed. Here, we refine the statistical methodology by Pérez-Montero et al. (2011) to probe the presence of variations in the ISM properties. An error-weighted mean of 12+log(O/H) = 7.72 ± 0.01 is taken as the representative oxygen abundance for Mrk 178. A localized N and He enrichment, spatially correlated with WR stars, is suggested by this analysis. Nebular He II λ4686 emission is shown to be spatially extended reaching well beyond the location of the WR stars. This spatial offset between WRs and He II emission can be explained based on the mechanical energy input into the ISM by the WR star winds, and does not rule out WR stars as the He II ionization source. We study systematic aperture effects on the detection and measurement of the WR features, using Sloan Digital Sky Survey spectra combined with the power of IFS. In this regard, the importance of targeting low metallicity nearby systems is discussed
Recommended from our members
Integrated Photoelectric Magnitudes And Color Indexes Of Bright Galaxies In The Johnson UBV System
Astronom