Publications (8)0 Total impact
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ABSTRACT: Super star clusters (SSCs) are typically found in interacting galaxies and
trace an extreme form of star-formation. We present a K-band study of SSC
candidates in a sample of local luminous infrared galaxies (LIRGs) using two
adaptive optics instruments (VLT/NACO and Gemini/ALTAIR/NIRI). In addition to
facilitating SSC detections in obscured environments, this work introduces SSC
studies in hosts with higher star-formation rates (SFRs) than most previous
studies. We find that the luminosity functions (LFs) of the clusters are
reasonably well-fitted by a single power-law with the values of the index
\alpha ranging between 1.5 to 2.4 with an average value of \alpha ~ 1.9. This
value appears to be less steep than the average \alpha ~ 2.2 in normal spiral
galaxies. Due to the host galaxy distances involved (median $D_L$ ~ 70 Mpc)
blending effects have to be taken into account, and are investigated using
Monte Carlo simulations of blending effects for LFs and a photometric SSC
analysis of the well-studied Antennae system which is artificially redshifted
to distances of our sample. While blending tends to flatten LFs our analyses
show that \Delta \alpha is less than ~ 0.1 in our sample. The simulations also
show that in the luminosity range, $M_K < -13$, considered in this work the
extracted SSC luminosities are generally dominated by a single dominant star
cluster rather than several knots of SF. We present resolution- and
distance-dependent SSC surface density confusion limits and show how blending
rates and aperture sizes affect the LFs. The smallest possible apertures should
be used in crowded regions.
02/2013;
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ABSTRACT: We study star formation (SF) in very active environments, in luminous IR
galaxies, which are often interacting. A variety of phenomena are detected,
such as central starbursts, circumnuclear SF, obscured SNe tracing the history
of recent SF, massive super star clusters, and sites of strong off-nuclear SF.
All of these can be ultimately used to define the sequence of triggering and
propagation of star-formation and interplay with nuclear activity in the lives
of gas rich galaxy interactions and mergers. In this paper we present analysis
of high-spatial resolution integral field spectroscopy of central regions of
two interacting LIRGs. We detect a nuclear 3.3 um PAH ring around the core of
NGC 1614 with thermal-IR IFU observations. The ring's characteristics and
relation to the strong star-forming ring detected in recombination lines are
presented, as well as a scenario of an outward expanding starburst likely
initiated with a (minor) companion detected within a tidal feature. We then
present NIR IFU observations of IRAS 19115-2124, aka the Bird, which is an
intriguing triple encounter. The third component is a minor one, but,
nevertheless, is the source of 3/4 of the SFR of the whole system. Gas inflows
and outflows are detected at the locations of the nuclei. Finally, we briefly
report on our on-going NIR adaptive optics imaging survey of several dozen
LIRGs. We have detected highly obscured core-collapse SNe in the central kpc,
and discuss the statistics of "missing SNe" due to dust extinction. We are also
determining the characteristics of hundreds of super star clusters in and
around the core regions of LIRGs, as a function of host-galaxy properties.
02/2012;
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ABSTRACT: The Extragalactic Background Light (EBL) at UV, optical and NIR wavelengths
consists of the integrated light of all unresolved galaxies along the line of
sight plus any contributions by intergalactic matter including hypothetical
decaying relic particles. The measurement of the EBL has turned out to be a
tedious problem. This is because of the foreground components of the night sky
brightness, much larger than the EBL itself: the Zodiacal Light (ZL),
Integrated Starlight (ISL), Diffuse Galactic Light (DGL) and, for ground-based
observations, the Airglow (AGL) and the tropospheric scattered light. We have
been developing a method for the EBL measurement which utilises the screening
effect of a dark nebula on the EBL. A differential measurement in the direction
of a high-latitude dark nebula and its surrounding area provides a signal that
is due to two components only, i.e. the EBL and the diffusely scattered ISL
from the cloud. We present a progress report of this method where we are now
utilising intermediate resolution spectroscopy with ESO's VLT telescope. We
detect and remove the scattered ISL component by using its characteristic
Fraunhofer line spectral signature. In contrast to the ISL, in the EBL spectrum
all spectral lines are washed out. We present a high quality spectrum
representing the difference between an opaque position within our target cloud
and several clear OFF positions around the cloud. We derive a preliminary EBL
value at 400 nm and an upper limit to the EBL at 520 nm. These values are in
the same range as the EBL lower limits derived from galaxy counts.
11/2011;
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ABSTRACT: It is important to understand the interplay between nuclear star-formation
and nuclear activity when studying the evolution of gas rich galaxy mergers. We
present here new spatially resolved L-band integral field unit observations of
the inner kpc of the luminous IR galaxy NGC 1614. A broad ring of 3.3 um PAH
emission is found at a distance of approximately 200 pc from the core. This
ring overlaps with a previously established star-forming ring detected with
Pa_alpha and radio continuum observations, but peaks outside it, especially if
determined using the PAH equivalent width. Using the characteristics of the PAH
emission and the ionised gas emission we argue that NGC 1614 features an
outward propagating ring of star formation, where the equivalent width of the
PAH emission localises the regions where the current star formation is just
expanding into the molecular gas outward of the nucleus. The core itself shows
a highly luminous, slightly resolved (at ~80 pc) L-band continuum source. We
find no evidence of AGN activity and rule out the presence of an obscured AGN
using L-band diagnostics. Furthermore, we detect the likely companion galaxy
from archival HST/ACS imaging. The star formation and dynamical characteristics
of the system are consistent with a relatively major merger just after its
second passage. An outstanding question is how a gas-rich advanced merger such
as this one, with strong LIRG level nuclear starburst and major merger-like
tidal features, has not yet developed an active nucleus.
11/2011;
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ABSTRACT: This work studies the environments and star formation relationships of local
luminous infrared galaxies (LIRG) in comparison to other types of local and
distant (z~1) galaxies. The infrared (IR) galaxies are drawn from the IRAS
sample. The density of the environment is quantified using 6dF and Point Source
Catalogue redshift survey (PSCz) galaxies in a cylinder of 2h^-1 Mpc radius and
10h^-1 Mpc length. Our most important result shows the existence of a dramatic
density difference between local LIRGs and local non-LIRG IR galaxies. LIRGs
live in denser environments than non-LIRG IR galaxies implying that L_IR=10^11
h^-2 L_sun marks an important transition point among IR-selected local
galaxies. We also find that there is a strong correlation between the densities
around LIRGs and their L_IR luminosity, while the IR-activity of non-LIRG IR
galaxies does not show any dependence on environment. This trend is independent
of mass-bin selection. The SF-density trend in local LIRGs is similar to that
found in some studies of blue cloud galaxies at z~1 which show a correlation
between star formation and local density (the reversal of the relation seen for
local galaxies). This, together with the rapid decline of the number count of
LIRGs since z~1, could mean that local LIRGs are survivors of whatever process
transformed blue cloud galaxies at z~1 to the present day or local LIRGs came
into existence by similar process than high redshift LIRGs but at later stage.
01/2011;
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ABSTRACT: We report on an on-going near-IR adaptive optics survey targeting interacting luminous IR galaxies. High-spatial resolution NIR data are crucial to enable interpretation of kinematic, dynamical and star formation (SF) properties of these very dusty objects. Whole progenitor nuclei in the interactions can be missed if only optical HST imaging is used. Here we specifically present the latest results regarding core-collapse supernovae found within the highly extincted nuclear regions of these galaxies. Direct detection and study of such highly obscured CCSNe is crucial for revising the optically-derived SN rates used for providing an independent measurement of the SF history of the Universe. We also present thus-far the first NIR luminosity functions of super star cluster (SSC) candidates. The LFs can then be used to constrain the formation and evolution of SSCs via constraints based on initial mass functions and cluster disruption models. Comment: 6 pages. To appear in proceedings of 'Galaxies and their Masks' (Namibia, April 2010), published by Springer, New York, eds. D.L. Block, K.C. Freeman, I. Puerari
09/2010;
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ABSTRACT: Near infrared adaptive optics observations are crucial to be able to interpret kinematic and dynamical data and study star formation properties within the often extremely dusty interacting luminous IR galaxies (LIRGs). NIR AO data are also needed to find supernovae in their bright and dusty central regions and to fully characterize the young stellar clusters found in these kinds of systems. We have used AO in the K-band to survey a sample of LIRGs at 0.1 arcsec (30 to 100 pc) resolution. The data are merged with SALT and AAT spectroscopic follow-up and HST and Spitzer archival imaging. The first AO detected SNe are reported as well as details of the first studied LIRGs. One LIRG showed an unexpected third component in the interaction, which moreover turned out to host the most active star formation. Another target showed evidence in the NIR of a very rare case of leading spiral arms, rotating in the same direction as the arms open. Comment: To appear in the proceedings of Galaxy Wars: Stellar populations and star formation in interacting galaxies
08/2009;
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ABSTRACT: Leading spiral arms are a rare phenomenon. We present here one of the very few convincing candidates of spiral arms opening counter-intuitively in the same direction as the galaxy disk is rotating. This detection in a luminous IR galaxy (LIRG) IRAS 18293-3134 is based on near infrared (NIR) adaptive optics imaging with the Very Large Telescope and long-slit NIR spectroscopy with the Anglo-Australian Telescope. We discuss the orientation of the galaxy based on imaging and derive rotation curves from both emission and absorption features in the spectrum. The galaxy is strongly star-forming and has a minor companion in a high-velocity encounter. The fact that the arms of IRAS 18293-3134 are not easily traceable from optical images suggests that larger samples of high-quality NIR imaging of interacting systems and LIRGs might uncover further cases of leading arms, placing constraints on spiral arm theories and retrograde encounters, and especially on the relationship between disk masses and dark matter halo masses. Comment: Accepted for publication in Astrophysical Journal Letters. 13 pages, 4 figures
10/2008;
