16 research outputs found
Formation of young massive star clusters: a high-resolution multi-wavelength study of intensely star-formation galaxies
Super star clusters (SSCs) represent the youngest and most massive form of known gravitationally bound star clusters in the Universe. They are born abundantly in environments that trigger strong and violent star formation (SF) such as in galaxy mergers and interacting systems. SSCs are thus used as fundamental tools to understand the context of massive SF and galaxy evolution in general. This thesis investigates properties of these young, massive and dense star clusters in a sample of 42 nearby starbursts and luminous infrared galaxies (LIRGs) ..
Super star cluster candidates in the star-forming regions of luminous infrared galaxies
Includes abstract.Includes bibliographical references (leaves 86-90).We report on a study of super star cluster (SSC) candidates in the star-forming regions of a representative sample of local luminous infrared galaxies (LIRGs) using KS-band near-infrared (NIR) adaptive optics imaging with GEMINI/ALTAIR and VLT/NACO instruments. The evolution of the cosmic star formation rate (CSFR) indicates its rapid decline in the local Universe
Near-infrared adaptive optics imaging of infrared luminous galaxies: the brightest cluster magnitude - star formation rate relation
We have established a relation between the brightest super star cluster
magnitude in a galaxy and the host star formation rate (SFR) for the first time
in the near infrared (NIR). The data come from a statistical sample of ~ 40
luminous IR galaxies (LIRGs) and starbursts utilizing K-band adaptive optics
imaging. While expanding the observed relation to longer wavelengths, less
affected by extinction effects, it also pushes to higher SFRs. The relation we
find, M_K ~ - 2.6 log SFR, is similar to that derived previously in the optical
and at lower SFRs. It does not, however, fit the optical relation with a single
optical to NIR color conversion, suggesting systematic extinction and/or age
effects. While the relation is broadly consistent with a size-of-sample
explanation, we argue physical reasons for the relation are likely as well. In
particular, the scatter in the relation is smaller than expected from pure
random sampling strongly suggesting physical constraints. We also derive a
quantifiable relation tying together cluster-internal effects and host SFR
properties to possibly explain the observed brightest SSC magnitude vs. SFR
dependency.Comment: 6 pages, 4 figures, accepted for publication in ApJ Letter
Star formation and AGN activity in a sample of local Luminous Infrared Galaxies through multi-wavelength characterization
Nuclear starbursts and AGN activity are the main heating processes in
luminous infrared galaxies (LIRGs) and their relationship is fundamental to
understand galaxy evolution. In this paper, we study the star-formation and AGN
activity of a sample of 11 local LIRGs imaged with subarcsecond angular
resolution at radio (8.4GHz) and near-infrared (m) wavelengths. This
allows us to characterize the central kpc of these galaxies with a spatial
resolution of pc. In general, we find a good spatial correlation
between the radio and the near-IR emission, although radio emission tends to be
more concentrated in the nuclear regions. Additionally, we use an MCMC code to
model their multi-wavelength spectral energy distribution (SED) using template
libraries of starburst, AGN and spheroidal/cirrus models, determining the
luminosity contribution of each component, and finding that all sources in our
sample are starburst-dominated, except for NGC6926 with an AGN contribution of
\%. Our sources show high star formation rates ( to
), supernova rates (0.4 to
), and similar starburst ages (13 to
), except for the young starburst (9Myr) in NGC6926. A
comparison of our derived star-forming parameters with estimates obtained from
different IR and radio tracers shows an overall consistency among the different
star formation tracers. AGN tracers based on mid-IR, high-ionization line
ratios also show an overall agreement with our SED model fit estimates for the
AGN. Finally, we use our wide-band VLA observations to determine pixel-by-pixel
radio spectral indices for all galaxies in our sample, finding a typical median
value () for synchrotron-powered LIRGs.Comment: Accepted for publication in MNRAS. 20 pages, 12 figure
Spectral age distribution for radio-loud active galaxies in the XMM-LSS field
Jets of energetic particles, as seen in FR type-I and FR type-II sources,
ejected from the center of Radio-Loud AGN affect the sources surrounding
intracluster medium/intergalactic medium. Placing constraints on the age of
such sources is important in order to measure the jet powers and determine the
effects on feedback. To evaluate the age of these sources using spectral age
models, we require high-resolution multi-wavelength data. The new sensitive and
high-resolution MIGHTEE survey of the XMM-LSS field along with data from the
Low Frequency Array (LOFAR) and the Giant Metrewave Radio Telescope (GMRT)
provide data taken at different frequencies with similar resolution, which
enables us to determine the spectral age distribution for radio loud AGN in the
survey field. In this study we present a sample of 28 radio galaxies with their
best fitting spectral age distribution analyzed using the Jaffe-Perola (JP)
model on a pixel-by-pixel basis. Fits are generally good and objects in our
sample show maximum ages within the range of 2.8 Myr to 115 Myr with a median
of 8.71 Myr. High-resolution maps over a range of frequencies are required to
observe detailed age distributions for small sources and high-sensitivity maps
will be needed in order to observe fainter extended emission. We do not observe
any correlation between the total physical size of the sources and their age
and we speculate both dynamical models and the approach to spectral age
analysis may need some modification to account for our observations.Comment: 20 pages, 9 figure
Molecular Gas and Star Formation Properties in Early Stage Mergers:SMA CO(2-1) Observations of the LIRGs NGC 3110 and NGC 232
Mergers of galaxies are an important mode for galaxy evolution because they
serve as an efficient trigger of powerful starbursts. However, observational
studies of the molecular gas properties during their early stages are scarce.
We present interferometric CO(2-1) maps of two luminous infrared galaxies
(LIRGs), NGC 3110 and NGC 232, obtained with the Submillimeter Array (SMA) with
~ 1 kpc resolution. While NGC 3110 is a spiral galaxy interacting with a minor
(14:1 stellar mass) companion, NGC 232 is interacting with a similarly sized
object. We find that such interactions have likely induced in these galaxies
enhancements in the molecular gas content and central concentrations, partly at
the expense of atomic gas. The obtained molecular gas surface densities in
their circumnuclear regions are M
pc, higher than in non-interacting objects by an order of magnitude. Gas
depletion times of ~ 0.5 - 1 Gyr are found for the different regions, lying in
between non-interacting disk galaxies and the starburst sequence. In the case
of NGC 3110, the spiral arms show on average 0.5 dex shorter depletion times
than in the circumnuclear regions if we assume a similar H-CO conversion
factor. We show that even in the early stages of the interaction with a minor
companion, a starburst is formed along the circumnuclear region and spiral
arms, where a large population of SSCs is found (~350), and at the same time a
large central gas concentration is building up which might be the fuel for an
active galactic nucleus. The main morphological properties of the NGC 3110
system are reproduced by our numerical simulations and allow us to estimate
that the current epoch of the interaction is at ~ 150 Myrs after closest
approach.Comment: 30 pages. Accepted for publication in Ap