89 research outputs found
Spatially Resolved [FeII] 1.64 \mu m Emission in NGC 5135. Clues for Understanding the Origin of the Hard X-rays in Luminous Infrared Galaxies
Spatially resolved near-IR and X-ray imaging of the central region of the
Luminous Infrared Galaxy NGC 5135 is presented. The kinematical signatures of
strong outflows are detected in the [FeII]1.64 \mu m emission line in a compact
region at 0.9 kpc from the nucleus. The derived mechanical energy release is
consistent with a supernova rate of 0.05-0.1 yr. The apex of the
outflowing gas spatially coincides with the strongest [FeII] emission peak and
with the dominant component of the extranuclear hard X-ray emission. All these
features provide evidence for a plausible direct physical link between
supernova-driven outflows and the hard X-ray emitting gas in a LIRG. This
result is consistent with model predictions of starbursts concentrated in small
volumes and with high thermalization efficiencies. A single high-mass X-ray
binary (HMXB) as the major source of the hard X-ray emission although not
favoured, cannot be ruled out. Outside the AGN, the hard X-ray emission in NGC
5135 appears to be dominated by the hot ISM produced by supernova explosions in
a compact star-forming region, and not by the emission due to HMXB. If this
scenario is common to U/LIRGs, the hard X-rays would only trace the most
compact (< 100 pc) regions with high supernova and star formation densities,
therefore a lower limit to their integrated star formation. The SFR derived in
NGC 5135 based on its hard X-ray luminosity is a factor of two and four lower
than the values obtained from the 24 \mu m and soft X-ray luminosities,
respectively.Comment: Accepted for Publication in ApJ, 18 pages, 2 figure
Type-2 Fuzzy Entropy-Sets
The final goal of this study is to adapt the concept of fuzzy entropy of De Luca and Termini to deal with Type-2 Fuzzy Sets. We denote this concept Type-2 Fuzzy Entropy-Set. However, the construction of the notion of entropy measure on an infinite set, such us [0, 1], is not effortless. For this reason, we first introduce the concept of quasi-entropy of a Fuzzy Set on the universe [0, 1]. Furthermore, whenever the membership function of the considered Fuzzy Set in the universe [0, 1] is continuous, we prove that the quasi-entropy of that set is a fuzzy entropy in the sense of De Luca y Termini. Finally, we present an illustrative example where we use Type-2 Fuzzy Entropy-Sets instead of fuzzy entropies in a classical fuzzy algorithm
Predicting Future Space Near-IR Grism Surveys using the WFC3 Infrared Spectroscopic Parallels Survey
We present near-infrared emission line counts and luminosity functions from
the HST WFC3 Infrared Spectroscopic Parallels (WISP) program for 29 fields
(0.037 deg^2) observed using both the G102 and G141 grisms. Altogether we
identify 1048 emission line galaxies with observed equivalent widths greater
than 40 Angstroms, 467 of which have multiple detected emission lines. The WISP
survey is sensitive to fainter flux levels (3-5x10^-17 ergs/s/cm^2) than the
future space near-infrared grism missions aimed at baryonic acoustic
oscillation cosmology (1-4x10^-16 ergs/s/cm^2), allowing us to probe the
fainter emission line galaxies that the shallower future surveys may miss.
Cumulative number counts of 0.7<z<1.5 galaxies reach 10,000 deg^-2 above an
H-alpha flux of 2x10^-16 ergs/s/cm^2. H-alpha-emitting galaxies with comparable
[OIII] flux are roughly 5 times less common than galaxies with just H-alpha
emission at those flux levels. Galaxies with low H-alpha/[OIII] ratios are very
rare at the brighter fluxes that future near-infrared grism surveys will probe;
our survey finds no galaxies with H-alpha/[OIII] < 0.95 that have H-alpha flux
greater than 3x10^-16 ergs/s/cm^2. Our H-alpha luminosity function contains a
comparable number density of faint line emitters to that found by the NICMOS
near-infrared grism surveys, but significantly fewer (factors of 3-4 less) high
luminosity emitters. We also find that our high redshift (z=0.9-1.5) counts are
in agreement with the high redshift (z=1.47) narrow band H-alpha survey of
HiZELS (Sobral et al. 2013), while our lower redshift luminosity function
(z=0.3-0.9) falls slightly below their z=0.84 result. The evolution in both the
H-alpha luminosity function from z=0.3--1.5 and the [OIII] luminosity function
from z=0.7-2.3 is almost entirely in the L* parameter, which steadily increases
with redshift over those ranges.Comment: 18 pages, 14 figures, Accepted by Ap
The globular cluster system of NGC 1316. II - The extraordinary object SH2
SH2 has been described as an isolated HII-region, located about 6.5 arcmin
south of the nucleus of NGC 1316 (Fornax A), a merger remnant in the the
outskirts of the Fornax cluster of galaxies. We give a first, preliminary
description of the stellar content and environment of this remarkable object.
We used photometric data in the Washington system and HST photometry from the
Hubble Legacy Archive for a morphological description and preliminary aperture
photometry. Low-resolution spectroscopy provides radial velocities of the
brightest star cluster in SH2 and a nearby intermediate-age cluster. SH2 is not
a normal HII-region, ionized by very young stars. It contains a multitude of
star clusters with ages of approximately 0.1 Gyr. A ring-like morphology is
striking. SH2 seems to be connected to an intermediate-age massive globular
cluster with a similar radial velocity, which itself is the main object of a
group of fainter clusters. Metallicity estimates from emission lines remain
ambiguous. The present data do not yet allow firm conclusions about the nature
or origin of SH2. It might be a dwarf galaxy that has experienced a burst of
extremely clustered star formation. We may witness how globular clusters are
donated to a parent galaxy.Comment: 5 pages, to appear in A&A, format slightly different from the printed
versio
Hubble Space Telescope Grism Spectroscopy of Extreme Starbursts Across Cosmic Time: The Role of Dwarf Galaxies in the Star Formation History of the Universe
Near infrared slitless spectroscopy with the Wide Field Camera 3, onboard the
Hubble Space Telescope, offers a unique opportunity to study low-mass galaxy
populations at high-redshift (1-2). While most high surveys are
biased towards massive galaxies, we are able to select sources via their
emission lines that have very-faint continua. We investigate the star formation
rate (SFR)-stellar mass () relation for about 1000 emission-line
galaxies identified over a wide redshift range of . We use the H emission as an accurate SFR indicator and correct
the broadband photometry for the strong nebular contribution to derive accurate
stellar masses down to . We focus here on a
subsample of galaxies that show extremely strong emission lines (EELGs) with
rest-frame equivalent widths ranging from 200 to 1500 \AA. This population
consists of outliers to the normal SFR- sequence with much higher
specific SFRs ( Gyr). While on-sequence galaxies follow a
continuous star formation process, EELGs are thought to be caught during an
extreme burst of star formation that can double their stellar mass in less than
Myr. The contribution of starbursts to the total star formation density
appears to be larger than what has been reported for more massive galaxies in
previous studies. In the complete mass range log()
and a SFR lower completeness limit of about 2 yr (10
yr) at (), we find that starbursts having
EW(H) 300, 200, and 100 A contribute up to , 18,
and 34 %, respectively, to the total SFR of emission-line selected sample at
. The comparison with samples of massive galaxies shows an increase
in the contribution of starbursts towards lower masses.Comment: 11 pages, 6 figures. The Astrophysical Journal, in pres
Physical Properties of Emission-Line Galaxies at z ~ 2 from Near-Infrared Spectroscopy with Magellan FIRE
We present results from near-infrared spectroscopy of 26 emission-line
galaxies at z ~ 2 obtained with the FIRE spectrometer on the Magellan Baade
telescope. The sample was selected from the WISP survey, which uses the
near-infrared grism of the Hubble Space Telescope Wide Field Camera 3 to detect
emission-line galaxies over 0.3 < z < 2.3. Our FIRE follow-up spectroscopy
(R~5000) over 1.0-2.5 micron permits detailed measurements of physical
properties of the z~2 emission-line galaxies. Dust-corrected star formation
rates for the sample range from ~5-100 M_sun yr-1. We derive a median
metallicity for the sample of ~0.45 Z_sun, and the estimated stellar masses
range from ~10^8.5 - 10^9.5 M_sun. The average ionization parameters measured
for the sample are typically much higher than what is found for local
star-forming galaxies. We derive composite spectra from the FIRE sample, from
which we infer typical nebular electron densities of ~100-400 cm^-3. Based on
the location of the galaxies and composite spectra on BPT diagrams, we do not
find evidence for significant AGN activity in the sample. Most of the galaxies
as well as the composites are offset in the BPT diagram toward higher [O
III]/H-beta at a given [N II]/H-alpha, in agreement with other observations of
z > 1 star-forming galaxies, but composite spectra derived from the sample do
not show an appreciable offset from the local star-forming sequence on the [O
III]/H-beta versus [S II]/H-alpha diagram. We infer a high nitrogen-to-oxygen
abundance ratio from the composite spectrum, which may contribute to the offset
of the high-redshift galaxies from the local star-forming sequence in the [O
III]/H-beta versus [N II]/H-alpha diagram. We speculate that the elevated
nitrogen abundance could result from substantial numbers of Wolf-Rayet stars in
starbursting galaxies at z~2. (Abridged)Comment: Accepted for publication in Ap
Dust extinction from Balmer decrements of star-forming galaxies at 0.75<z<1.5 with HST/WFC3 spectroscopy from the WISP survey
Spectroscopic observations of Halpha and Hbeta emission lines of 128
star-forming galaxies in the redshift range 0.75<z<1.5 are presented. These
data were taken with slitless spectroscopy using the G102 and G141 grisms of
the Wide-Field-Camera 3 (WFC3) on board the Hubble Space Telescope as part of
the WFC3 Infrared Spectroscopic Parallel (WISP) survey. Interstellar dust
extinction is measured from stacked spectra that cover the Balmer decrement
(Halpha/Hbeta). We present dust extinction as a function of Halpha luminosity
(down to 3 x 10^{41} erg/s), galaxy stellar mass (reaching 4 x 10^{8} Msun),
and rest-frame Halpha equivalent width. The faintest galaxies are two times
fainter in Halpha luminosity than galaxies previously studied at z~1.5. An
evolution is observed where galaxies of the same Halpha luminosity have lower
extinction at higher redshifts, whereas no evolution is found within our error
bars with stellar mass. The lower Halpha luminosity galaxies in our sample are
found to be consistent with no dust extinction. We find an anti-correlation of
the [OIII]5007/Halpha flux ratio as a function of luminosity where galaxies
with L_{Halpha}<5 x 10^{41} erg/s are brighter in [OIII]5007 than Halpha. This
trend is evident even after extinction correction, suggesting that the
increased [OIII]5007/Halpha ratio in low luminosity galaxies is likely due to
lower metallicity and/or higher ionization parameters.Comment: 11 pages, 9 figures, 2 tables; version addressing the referee
comment
The globular cluster system of NGC1316. I. Wide-field photometry in the Washington system
NGC 1316 (Fornax A) is a prominent merger remnant in the outskirts of the
Fornax cluster. The cluster system has not yet been studied in its entirety. We
therefore present a wide-field study of the globular cluster system of NGC
1316, investigating its properties in relation to the global morphology of NGC
1316. We used the MOSAIC II camera at the 4-m Blanco telescope at CTIO in the
filters Washington C and Harris R. We identify globular cluster candidates and
study their color distribution and the structural properties of the system. In
an appendix, we also make morphological remarks, present color maps, and
present new models for the brightness and color profiles of the galaxy. The
cluster system is well confined to the optically visible outer contours of NGC
1316. The color distribution of the entire sample is unimodal, but the color
distribution of bright subsamples in the bulge shows two peaks that, by
comparison with theoretical Washington colors with solar metallicity,
correspond to ages of about 2 Gyr and 0.8 Gyr, respectively. We also find a
significant population of clusters in the color range 0.8 < C-R < 1.1 which
must be populated by clusters younger than 0.8 Gyr, unless they are very
metal-poor. The color interval 1.3 < C-R < 1.6 hosts the bulk of
intermediate-age clusters which show a surface density profile with a sharp
decline at about 4 arcmin. The outer cluster population shows an unimodal color
distribution with a peak at C-R=1.1, indicating a larger contribution of old,
metal-poor clusters. Their luminosity function does not show the expected
turn-over, so the fraction of younger clusters is still significant. Cluster
formation in NGC 1316 has continued after an initial burst, presumably related
to the main merger. A toy model with two bursts of ages 2 Gyr and 0.8 Gyr is
consistent with photometric properties and dynamical M/L-values.Comment: 19 pages, to appear in Astronomy and Astrophysics, abstract abridged,
format slightly different from the printed versio
VLT-VIMOS integral field spectroscopy of luminous and ultraluminous infrared galaxies II. Evidence for shock ionization caused by tidal forces in the extra-nuclear regions of interacting and merging LIRGs
LIRGs are an important class of objects in the low-z universe bridging the
gap between normal spirals and the strongly interacting and starbursting
ULIRGs. Studies of their 2D physical properties are still lacking. We aim to
understand the nature and origin of the ionization mechanisms operating in the
extranuclear regions of LIRGs as a function of the interaction phase and L_IR
by using IFS data obtained with VIMOS. Our analysis is based on over 25300
spectra of 32 LIRGs covering all types of morphologies and the entire
10^11-10^12 L_sun range. We found strong evidence for shock ionization, with a
clear trend with the dynamical status of the system. Specifically, we
quantified the variation with interaction phase of several line ratios
indicative of the excitation degree. While the [NII]/Ha ratio does not show any
significant change, the [SII]/Ha and [OI]/Ha ratios are higher for more
advanced interaction stages. We constrained the main mechanisms causing the
ionization in the extra-nuclear regions using diagnostic diagrams. Isolated
systems are mainly consistent with ionization caused by young stars. Large
fractions of the extra-nuclear regions in interacting pairs and more advanced
mergers are consistent with ionization caused by shocks. This is supported by
the relation between the excitation degree and the velocity dispersion of the
ionized gas, which we interpret as evidence for shock ionization in interacting
galaxies and advanced mergers but not in isolated galaxies. This relation does
not show any dependence with L_IR. All this indicates that tidal forces play a
key role in the origin of the ionizing shocks in the extra-nuclear regions. We
also showed what appears to be a common [OI]/Ha-sigma relation for the
extranuclear ionized gas in interacting (U)LIRGs. This needs to be investigated
further with a larger sample of ULIRGs.Comment: Accepted for publication in Astronomy and Astrophysics. Some figures
were removed due to space limitations. A version with the whole set of
figures can be seen at
http://www.damir.iem.csic.es/extragalactic/publications/publications.htm
- …