1,389 research outputs found
Star Formation Rate Indicators in Wide-Field Infrared Survey Preliminary Release
With the goal of investigating the degree to which theMIR luminosity in
theWidefield Infrared Survey Explorer (WISE) traces the SFR, we analyze 3.4,
4.6, 12 and 22 {\mu}m data in a sample of {\guillemotright} 140,000
star-forming galaxies or star-forming regions covering a wide range in
metallicity 7.66 < 12 + log(O/H) < 9.46, with redshift z < 0.4. These
star-forming galaxies or star-forming regions are selected by matching the WISE
Preliminary Release Catalog with the star-forming galaxy Catalog in SDSS DR8
provided by JHU/MPA 1.We study the relationship between the luminosity at 3.4,
4.6, 12 and 22 {\mu}m from WISE and H\alpha luminosity in SDSS DR8. From these
comparisons, we derive reference SFR indicators for use in our analysis. Linear
correlations between SFR and the 3.4, 4.6, 12 and 22 {\mu}m luminosity are
found, and calibrations of SFRs based on L(3.4), L(4.6), L(12) and L(22) are
proposed. The calibrations hold for galaxies with verified spectral
observations. The dispersion in the relation between 3.4, 4.6, 12 and 22 {\mu}m
luminosity and SFR relates to the galaxy's properties, such as 4000 {\deg}A
break and galaxy color.Comment: 10 pages, 3 figure
Total Infrared Luminosity Estimation of Resolved and Unresolved Galaxies
The total infrared (TIR) luminosity from galaxies can be used to examine both
star formation and dust physics. We provide here new relations to estimate the
TIR luminosity from various Spitzer bands, in particular from the 8 micron and
24 micron bands. To do so, we use 45" subregions within a subsample of nearby
face-on spiral galaxies from the Spitzer Infrared Nearby Galaxies Survey
(SINGS) that have known oxygen abundances as well as integrated galaxy data
from the SINGS, the Local Volume Legacy Survey (LVL) and Engelbracht et al.
(2008) samples. Taking into account the oxygen abundances of the subregions,
the star formation rate intensity, and the relative emission of the polycyclic
aromatic hydrocarbons at 8 micron, the warm dust at 24 micron and the cold dust
at 70 micron and 160 micron we derive new relations to estimate the TIR
luminosity from just one or two of the Spitzer bands. We also show that the
metallicity and the star formation intensity must be taken into account when
estimating the TIR luminosity from two wave bands, especially when data
longward of 24 micron are not available.Comment: 11 pages, 10 figures, accepted for publication in Ap
FUSE Observations of Outflowing OVI in the Dwarf Starburst Galaxy NGC1705
We report FUSE far-UV spectroscopy of the prototypical dwarf starburst galaxy
NGC 1705. These data allow us for the first time to probe the coronal-phase gas
(T = 10E5 to 10E6 K) that may dominate the radiative cooling of the
supernova-heated ISM and thereby determine the dynamical evolution of
starburst-driven outflows. We detect a broad (100 km/s) and blueshifted (by 80
km/s) OVI absorption-line arising in the previously-known galactic outflow. The
properties of the OVI absorption are inconsistent with the standard superbubble
model in which this gas arises in a conductive interface inside the outer
shell. We show that the superbubble in NGC 1705 is blowing out of the galaxy
ISM. During blow-out, coronal-phase gas can be created by hydrodynamical mixing
as hot gas rushes out through fissures in the fragmenting shell of cool gas. As
the coronal gas cools radiatively, it can naturally produce the observed OVI
column density and outflow speed. The OVI data show that the cooling rate in
the coronal-phase gas is less than about 10% of the supernova heating rate.
Since the X-ray luminosity from hotter gas is even smaller, we conclude that
radiative losses are insignificant. The outflow should be able to vent its
metals and kinetic energy out of the galaxy. This process has potentially
important implications for the evolution of dwarf galaxies and the IGM.Comment: ApJ (in press
CIRPASS near-infrared integral-field spectroscopy of massive star clusters in the starburst galaxy NGC 1140
[ABRIDGED] We analyse near-infrared integral field spectroscopy of the
central starburst region of NGC 1140, obtained at the Gemini-South telescope
equipped with CIRPASS. Our ~1.45-1.67 um wavelength coverage includes the
bright [Fe II] emission line, as well as high-order Brackett (hydrogen) lines.
While strong [Fe II] emission, thought to originate in the thermal shocks
associated with supernova remnants, is found throughout the galaxy, both Br
12-4 and Br 14-4 emission, and weak CO(6,3) absorption, is predominantly
associated with the northern starburst region. The Brackett lines originate
from recombination processes occurring on smaller scales in (young) HII
regions. The time-scale associated with strong [Fe II] emission implies that
most of the recent star-formation activity in NGC 1140 was induced in the past
35-55 Myr. Based on the spatial distributions of the [Fe II] versus Brackett
line emission, we conclude that a galaxy-wide starburst was induced several
tens of Myr ago, with more recent starburst activity concentrated around the
northern starburst region. This scenario is (provisionally) confirmed by our
analysis of the spectral energy distributions of the compact, young massive
star clusters (YMCs) detected in new and archival broad-band HST images. The
YMC ages in NGC 1140 are all <= 20 Myr, consistent with independently
determined estimates of the galaxy's starburst age, while there appears to be
an age difference between the northern and southern YMC complexes in the sense
expected from our CIRPASS analysis. Our photometric mass estimates of the NGC
1140 YMCs, likely upper limits, are comparable to those of the highest-mass
Galactic globular clusters and to spectroscopically confirmed masses of
(compact) YMCs in other starburst galaxies.Comment: 16 pages LaTeX, incl. 6 postscript figures; accepted for publication
in MNRA
On the Escape of Ionizing Radiation from Starbursts
Far-ultraviolet spectra obtained with show that the strong
1036 interstellar absorption-line is essentially black in five of
the UV-brightest local starburst galaxies. Since the opacity of the neutral ISM
below the Lyman-edge will be significantly larger than in the line, these
data provide strong constraints on the escape of ionizing radiation from these
starbursts. Interpreted as a a uniform absorbing slab, the implied optical
depth at the Lyman edge is huge (). Alternatively, the areal
covering factor of opaque material is typically 94%. Thus, the fraction
of ionizing stellar photons that escape the ISM of each galaxy is small: our
conservative estimates typically yield . Inclusion of
extinction due to dust will further decrease . An analogous analysis
of the rest-UV spectrum of the star-forming galaxy at =2.7
leads to similar constraints on . These new results agree with the
constraints provided by direct observations below the Lyman edge in a few other
local starbursts. However, they differ from the recently reported properties of
star-forming galaxies at 3. We assess the idea that the strong
galactic winds seen in many powerful starbursts clear channels through their
neutral ISM. We show empirically that such outflows may be a necessary - but
not sufficient - part of the process for creating a relatively porous ISM. We
note that observations will soon document the cosmic evolution in the
contribution of star-forming galaxies to the metagalactic ionizing background,
with important implications for the evolution of the IGM.Comment: 17 pages; ApJ, in pres
- …