799 research outputs found
Dust Attenuation Curves in the Local Universe: Demographics and New Laws for Star-forming Galaxies and High-redshift Analogs
We study dust attenuation curves of 230,000 individual galaxies in the local
universe, ranging from quiescent to intensely star-forming systems, using
GALEX, SDSS, and WISE photometry calibrated on Herschel-ATLAS. We use a new
method of constraining SED fits with infrared luminosity (SED+LIR fitting), and
parameterized attenuation curves determined with the CIGALE SED fitting code.
Attenuation curve slopes and UV bump strengths are reasonably well constrained
independently from one another. We find that attenuation
curves exhibit a very wide range of slopes that are on average as steep as the
SMC curve slope. The slope is a strong function of optical opacity. Opaque
galaxies have shallower curves - in agreement with recent radiate transfer
models. The dependence of slopes on the opacity produces an apparent dependence
on stellar mass: more massive galaxies having shallower slopes. Attenuation
curves exhibit a wide range of UV bump amplitudes, from none to MW-like; with
an average strength 1/3 of the MW bump. Notably, local analogs of high-redshift
galaxies have an average curve that is somewhat steeper than the SMC curve,
with a modest UV bump that can be to first order ignored, as its effect on the
near-UV magnitude is 0.1 mag. Neither the slopes nor the strengths of the UV
bump depend on gas-phase metallicity. Functional forms for attenuation laws are
presented for normal star-forming galaxies, high-z analogs and quiescent
galaxies. We release the catalog of associated SFRs and stellar masses
(GSWLC-2).Comment: Accepted to ApJ. GSWLC-2 catalog of SED+LIR SFRs and M* to be
released Jun 1 at http://pages.iu.edu/~salims/gswlc
DustKING, the story continues : dust attenuation in NGC 628
Dust attenuation is a crucial but highly uncertain parameter that hampers the determination of in- trinsic galaxy properties, such as stellar masses, star formation rates and star formation histories. The shape of the dust attenuation law is not expected to be uniform between galaxies, nor within a galaxy. Our DustKING project was introduced at the first BINA workshop in 2016 and aims to study the variations of dust attenuation curves in nearby galaxies. At the second BINA workshop in 2018, I presented the results of our pilot study for the spiral galaxy NGC 628. We find that the average attenuation law of this galaxy is characterised by a MW-like bump and a steep UV slope. Furthermore, we observe intriguing variations within the galaxy, with regions of high AV exhibiting a shallower attenuation curve. Finally, we discuss how our work might benefit from data taken with the UVIT from the Indian AstroSat mission
DustKING - the story continues: dust attenuation in NGC628
Dust attenuation is a crucial but highly uncertain parameter that hampers the
determination of intrinsic galaxy properties, such as stellar masses, star
formation rates and star formation histories. The shape of the dust attenuation
law is not expected to be uniform between galaxies, nor within a galaxy. Our
DustKING project was introduced at the first BINA workshop in 2016 and aims to
study the variations of dust attenuation curves in nearby galaxies. At the
second BINA workshop in 2018, I presented the results of our pilot study for
the spiral galaxy NGC628. We find that the average attenuation law of this
galaxy is characterised by a MW-like bump and a steep UV slope. Furthermore, we
observe intriguing variations within the galaxy, with regions of high
exhibiting a shallower attenuation curve. Finally, we discuss how our work
might benefit from data taken with the UVIT from the Indian AstroSat mission.Comment: 8 pages, 6 figures, Proceedings paper of the second Belgo-Indian
Network for Astronomy & astrophysics (BINA) workshop, accepted for
publication in the Bulletin de la Soci\'et\'e Royale des Sciences de Li\`eg
Intergalactic Star Formation
Star formation in interacting systems may take place in various locations,
from the dust--enshrouded core of Ultraluminous Infrared Galaxies to more
unusual places such as the debris of colliding galaxies expelled into the
intergalactic medium. Determining whether star-formation proceeds in the latter
environment, far from the parent galaxies, in a similar way as in spiral disks
has motivated the multi--wavelength study presented here. We collected VLA/HI,
UV/GALEX, optical Halpha and MIR/Spitzer images of a few nearby interacting
systems chosen for their prominent "intergalactic" star formation activity.
Preliminary results on the spectacular collisional HI ring around NGC 5291 are
presented.Comment: 4 pages, 1 fig., tp appear in conference proceedings "Studying Galaxy
Evolution with Spitzer and Herschel", eds. V. Charmandaris, D. Rigopoulou &
N. Kylafi
Ionization processes in a local analogue of distant clumpy galaxies: VLT MUSE IFU spectroscopy and FORS deep images of the TDG NGC 5291N
We present IFU observations with MUSE@VLT and deep imaging with FORS@VLT of a
dwarf galaxy recently formed within the giant collisional HI ring surrounding
NGC 5291. This TDG-like object has the characteristics of typical z=1-2
gas-rich spiral galaxies: a high gas fraction, a rather turbulent clumpy ISM,
the absence of an old stellar population, a moderate metallicity and star
formation efficiency. The MUSE spectra allow us to determine the physical
conditions within the various complex substructures revealed by the deep
optical images, and to scrutinize at unprecedented spatial resolution the
ionization processes at play in this specific medium. Starburst age, extinction
and metallicity maps of the TDG and surrounding regions were determined using
the strong emission lines Hbeta, [OIII], [OI], [NII], Halpha and [SII] combined
with empirical diagnostics. Discrimination between different ionization
mechanisms was made using BPT--like diagrams and shock plus photoionization
models. Globally, the physical conditions within the star--forming regions are
homogeneous, with in particular an uniform half-solar oxygen abundance. At
small scales, the derived extinction map shows narrow dust lanes. Regions with
atypically strong [OI] emission line immediately surround the TDG. The [OI] /
Halpha ratio cannot be easily accounted for by photoionization by young stars
or shock models. At larger distances from the main star--forming clumps, a
faint diffuse blue continuum emission is observed, both with the deep FORS
images and MUSE data. It does not have a clear counterpart in the UV regime
probed by GALEX. A stacked spectrum towards this region does not exhibit any
emission line, excluding faint levels of star formation, nor stellar absorption
lines that might have revealed the presence of old stars. Several hypotheses
are discussed for the origin of these intriguing features.Comment: 13 pages, 15 figures, accepted for publication in A&
Star Formation in Collision Debris: Insights from the modeling of their Spectral Energy Distribution
During galaxy-galaxy interactions, massive gas clouds can be injected into
the intergalactic medium which in turn become gravitationally bound, collapse
and form stars, star clusters or even dwarf galaxies. The objects resulting
from this process are both "pristine", as they are forming their first
generation of stars, and chemically evolved because the metallicity inherited
from their parent galaxies is high. Such characteristics make them particularly
interesting laboratories to study star formation. After having investigated
their star-forming properties, we use photospheric, nebular and dust modeling
to analyze here their spectral energy distribution (SED) from the
far-ultraviolet to the mid-infrared regime for a sample of 7 star-forming
regions. Our analysis confirms that the intergalactic star forming regions in
Stephan's Quintet, around Arp 105, and NGC 5291, appear devoid of stellar
populations older than 10^9 years. We also find an excess of light in the
near-infrared regime (from 2 to 4.5 microns) which cannot be attributed to
stellar photospheric or nebular contributions. This excess is correlated with
the star formation rate intensity suggesting that it is probably due to
emission by very small grains fluctuating in temperature as well as the
polycyclic aromatic hydrocarbons (PAH) line at 3.3 micron. Comparing the
attenuation via the Balmer decrement to the mid-infrared emission allows us to
check the reliability of the attenuation estimate. It suggests the presence of
embedded star forming regions in NGC 5291 and NGC 7252. Overall the SED of
star-forming regions in collision debris (and Tidal Dwarf Galaxies) resemble
more that of dusty star-forming regions in galactic disks than to that of
typical star-forming dwarf galaxies.Comment: 22 pages, 24 figures, accepted for publication in A
Tidal Debris posing as Dark Galaxies
Debris sent into the intergalactic medium during tidal collisions can tell us
about several fundamental properties of galaxies, in particular their missing
mass, both in the form of cosmological Dark Matter and so-called Lost Baryons.
High velocity encounters, which are common in clusters of galaxies, are able to
produce faint tidal debris that may appear as star-less, free floating HI
clouds. These may be mistaken for Dark Galaxies, a putative class of gaseous,
dark matter dominated, objects which for some reason never managed to form
stars. VirgoHI21 is by far the most spectacular and most discussed Dark Galaxy
candidate so far detected in HI surveys. We show here that it is most likely
made out of material expelled 750 Myr ago from the nearby spiral galaxy NGC
4254 during its fly--by at about 1000 km/s by a massive intruder. Our numerical
model of the collision is able to reproduce the main characteristics of the
system: in particular the absence of stars, and its prominent velocity
gradient. Originally attributed to the gas being in rotation within a massive
dark matter halo, we find it instead to be consistent with a combination of
simple streaming motion plus projection effects (Duc & Bournaud, 2007). We
discuss several ways to identify a tidal origin in a Dark Galaxy candidate and
illustrate the method using another HI system in Virgo, VCC 2062, which is most
likely a Tidal Dwarf Galaxy (Duc et al., 2007). Now, whereas tidal debris
should not contain any dark matter from the halo of their parent galaxies, it
may exhibit missing mass in the form of dark baryons, unaccounted for by
classical observations, as recently found in the collisional ring of NGC 5291
(Bournaud et al., 2007) and probably in the TDG VCC 2062. These "Lost Baryons"
must originally have been located in the disks of their parent galaxies.Comment: 10 pages, 4 figures, to appear in IAU symposium 244 "Dark Galaxies
and Lost Baryons
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