44 research outputs found
Integral field observations of the blue compact galaxy Haro14. Star formation and feedback in dwarf galaxies
(Abridged) Low-luminosity, gas-rich blue compact galaxies (BCG) are ideal
laboratories to investigate many aspects of the star formation in galaxies. We
study the morphology, stellar content, kinematics, and the nebular excitation
and ionization mechanism in the BCG Haro 14 by means of integral field
observations with VIMOS in the VLT. From these data we build maps in continuum
and in the brighter emission lines, produce line-ratio maps, and obtain the
velocity and velocity dispersion fields. We also generate the integrated
spectrum of the major HII regions and young stellar clusters identified in the
maps to determine reliable physical parameters and oxygen abundances. We find
as follows: i) the current star formation in Haro 14 is spatially extended with
the major HII regions placed along a linear structure, elongated in the
north-south direction, and in a horseshoe-like curvilinear feature that extends
about 760 pc eastward; the continuum emission is more concentrated and peaks
close to the galaxy center; ii) two different episodes of star formation are
present: the recent starburst, with ages 6 Myrs and the intermediate-age
clusters, with ages between 10 and 30 Myrs; these stellar components rest on a
several Gyr old underlying host galaxy; iii) the H/H pattern is
inhomogeneous, with excess color values varying from E(B-V)=0.04 up to
E(B-V)=1.09; iv) shocks play a significant role in the galaxy; and v) the
velocity field displays a complicated pattern with regions of material moving
toward us in the east and north galaxy areas. The morphology of Haro 14, its
irregular velocity field, and the presence of shocks speak in favor of a
scenario of triggered star formation. Ages of the knots are consistent with the
ongoing burst being triggered by the collective action of stellar winds and
supernovae originated in the central clusters.Comment: 18 pages, 17 figures. Accepted for publication in A&
Probing star formation and feedback in dwarf galaxies. Integral field view of the blue compact galaxy Tololo 1937-423
(Abridged) Blue compact galaxies (BCG) are gas-rich, low-mass, small systems
that form stars at unusually high rates. This makes them excellent laboratories
for investigating the process of star-formation (SF) at galactic scales and the
effects of massive stellar feedback on the interstellar (and intergalactic)
medium.
We analyzed the BCG Tololo 1937-423 using optical integral field spectroscopy
with VIMOS at the Very Large Telescope to probe its morphology, stellar
content, nebular excitation and ionization properties, and the kinematics of
its warm ionized gas.
We found that Tololo 1937-423 is currently undergoing an extended starburst,
with nine major clumps. The galaxy presents a single continuum peak
that is not cospatial with any knot in emission lines, indicating at least two
relatively recent episodes of SF. The inhomogeneous dust distribution reaches
its maximum roughly at the position of the continuum peak. We found shocked
regions in the galaxy outer regions and at the edges of the SF knots. The
oxygen abundance is similar in all the SF regions, suggesting a chemically
homogeneous ionized interstellar medium over spatial scales of several kpc. The
ionized gas kinematics displays an overall regular rotation around a
northwest-southeast axis.
The morphology of the galaxy and the two different episodes of SF suggest a
scenario of triggered (induced by supernova shock waves) SF acting in Tololo
1937-423. The inferred ages for the different SF episodes (~13-80 Myr for the
central post-starburst and 5-7 Myr for the ongoing SF) are consistent with
triggered SF, with the most recent SF episode caused by the collective effect
of stellar winds and supernova explosions from the central post-starburst. The
velocity dispersion pattern, with higher velocity dispersions found at the
edges of the SF regions, and shocked regions in the galaxy, also favor this
scenario.Comment: 16 pages, 18 figures. Accepted for publication in A&
Mapping Luminous Blue Compact Galaxies with VIRUS-P: morphology, line ratios and kinematics
[abridged] We carry out an integral field spectroscopy (IFS) study of a
sample of luminous BCGs, with the aim to probe the morphology, kinematics, dust
extinction and excitation mechanisms of their warm interstellar medium (ISM).
IFS data for five luminous BCGs were obtained using VIRUS-P, the prototype
instrument for the Visible Integral Field Replicable Unit Spectrograph,
attached to the 2.7m Harlan J. Smith Telescope at the McDonald Observatory.
VIRUS-P consists of a square array of 247 optical fibers, which covers a
109"x109" field of view, with a spatial sampling of 4.2" and a 0.3 filling
factor. We observed in the 3550-5850 Angstrom spectral range, with a resolution
of 5 A FWHM. From these data we built two-dimensional maps of the continuum and
the most prominent emission-lines ([OII]3727, Hgamma, Hbeta and [OIII]5007),
and investigate the morphology of diagnostic emission-line ratios and the
extinction patterns in the ISM as well as stellar and gas kinematics.
Additionally, from integrated spectra we infer total line fluxes and
luminosity-weighted extinction coefficients and gas-phase metallicities. All
galaxies exhibit an overall regular morphology in the stellar continuum, while
their warm ISM morphology is more complex: in II Zw 33 and Mrk 314, the
star-forming regions are aligned along a chain-structure; Haro 1, NGC 4670 and
III Zw 102 display several salient features, such as extended gaseous filaments
and bubbles. A significant intrinsic absorption by dust is present in all
galaxies, the most extreme case being III Zw 102. Our data reveal a manifold of
kinematical patterns, from overall regular gas and stellar rotation to complex
velocity fields produced by structurally and kinematically distinct components.Comment: Accepted for publication in A&A. 16 pages, 10 figure
Understanding star formation and feedback in small galaxies. The case of the blue compact dwarf Mrk 900
(Abridged) Low-luminosity, active star-forming blue compact galaxies (BCGs)
are excellent laboratories for investigating the process of star formation on
galactic scales and probing the interplay between massive stars and the
surrounding interstellar (or intergalactic) medium. We investigated the
morphology, structure, and stellar content of the Blue Compact Galaxy Mrk 900,
combining optical integral field observations obtained with VIMOS at the VLT
and deep broad-band photometry taken at the 2.5 m NOT telescope. From the
integral field data, we built continuum, emission, and diagnostic line ratio
maps and produced velocity and velocity dispersion maps. We also generated the
integrated spectrum of the major HII regions and the nuclear area to determine
reliable physical parameters and oxygen abundances. The broad-band data,
tracing the galaxy up to radius 4 kpc, allowed us to investigate the properties
of the low surface brightness underlying stellar host. We disentangle two
different stellar components in Mrk 900: a young population, which resolves
into individual stellar clusters with ages ~5.5-6.6 Myr and extends about 1 kpc
along the galaxy minor axis, is placed on top of a rather red and regular
shaped underlying stellar host, several Gyr old. We find evidence of a
substantial amount of dust and an inhomogeneous extinction pattern, with a dust
lane crossing the central starburst. Mrk 900 displays overall rotation,
although distorted in the central, starburst regions; the dispersion velocity
map is highly inhomogeneous, with values increasing up to 60 kms at the
periphery of the SF regions, where we also find hints of the presence of
shocks. Our observational results point to an interaction or merger with a
low-mass object or infalling gas as plausible trigger mechanisms for the
present starburst event.Comment: 17 pages, 19 figures. Accepted for publication in A&
The stellar host in blue compact dwarf galaxies: the need for a two-dimensional fit
The structural properties of the low surface brightness stellar host in blue
compact dwarf galaxies are often studied by fitting r^{1/n} models to the outer
regions of their radial profiles. The limitations imposed by the presence of a
large starburst emission overlapping the underlying component makes this kind
of analysis a difficult task. We propose a two-dimensional fitting methodology
in order to improve the extraction of the structural parameters of the LSB
host. We discuss its advantages and weaknesses by using a set of simulated
galaxies and compare the results for a sample of eight objects with those
already obtained using a one-dimensional technique. We fit a PSF convolved
Sersic model to synthetic galaxies, and to real galaxy images in the B, V, R
filters. We restrict the fit to the stellar host by masking out the starburst
region and take special care to minimize the sky-subtraction uncertainties. In
order to test the robustness and flexibility of the method, we carry out a set
of fits with synthetic galaxies. Furthermore consistency checks are performed
to assess the reliability and accuracy of the derived structural parameters.
The more accurate isolation of the starburst emission is the most important
advantage and strength of the method. Thus, we fit the host galaxy in a range
of surface brightness and in a portion of area larger than in previous
published 1D fits with the same dataset. We obtain robust fits for all the
sample galaxies, all of which, except one, show Sersic indices n very close to
1, with good agreement in the three bands. These findings suggest that the
stellar hosts in BCDs have near-exponential profiles, a result that will help
us to understand the mechanisms that form and shape BCD galaxies, and how they
relate to the other dwarf galaxy classes.Comment: 22 pages, 15 figures (low resolution), accepted for publication in
A&A. A higher resolution version of the figures can be provided upon reques
Mapping the properties of blue compact dwarf galaxies: integral field spectroscopy with PMAS
(Abridged) We perform integral field spectroscopy of a sample of Blue compact
dwarf (BCD) galaxies with the aim of analyzing their morphology, the spatial
distribution of some of their physical properties (excitation, extinction, and
electron density) and their relationship with the distribution and evolutionary
state of the stellar populations. Integral field spectroscopy observations of
the sample galaxies were carried out with the Potsdam Multi-Aperture
Spectrophotometer (PMAS) at the 3.5 m telescope at Calar Alto Observatory. An
area 16 arcsec x 16 arcsec in size was mapped with a spatial sampling of 1
arcsec x 1 arcsec. We obtained data in the 3590-6996 Angstroms spectral range,
with a linear dispersion of 3.2 Angstroms per pixel. From these data we built
two-dimensional maps of the flux of the most prominent emission lines, of two
continuum bands, of the most relevant line ratios, and of the gas velocity
field. Integrated spectra of the most prominent star-forming regions and of
whole objects within the FOV were used to derive their physical parameters and
the gas metal abundances. Six galaxies display the same morphology both in
emission line and in continuum maps; only in two objects, Mrk 32 and Tololo
1434+032, the distributions of the ionized gas and of the stars differ
considerably. In general the different excitation maps for a same object
display the same pattern and trace the star-forming regions, as expected for
objects ionized by hot stars; only the outer regions of Mrk 32, I Zw 123 and I
Zw 159 display higher [SII]/Halpha values, suggestive of shocks. Six galaxies
display an inhomogeneous dust distribution. Regarding the kinematics, Mrk 750,
Mrk 206 and I Zw 159 display a clear rotation pattern, while in Mrk 32, Mrk 475
and I Zw 123 the velocity fields are flat.Comment: 27 pages, 11 figures; Accepted for publication in A&
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Warm ionized gas in the blue compact galaxy Haro 14 viewed by MUSE
We investigate the warm ionized gas in the blue compact galaxy (BCG) Haro 14 by means of integral field spectroscopic observations taken with the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope. The large field of view of MUSE and its unprecedented sensitivity enable observations of the galaxy nebular emission up to large galactocentric distances, even in the important but very faint [O i] λ6300 diagnostic line. This allowed us to trace the ionized gas morphology and ionization structure of Haro 14 up to kiloparsec scales and, for the first time, to accurately investigate the excitation mechanism operating in the outskirts of a typical BCG. The intensity and diagnostic maps reveal at least two highly distinct components of ionized gas: the bright central regions, mostly made of individual clumps, and a faint component which extends up to kiloparsec scales and consists of widespread diffuse emission, well-delineated filamentary structures, and faint knots. Noteworthy are the two curvilinear filaments extending up to 2 and 2.3 kpc southwest, which likely trace the edges of supergiant expanding bubbles driven by galactic outflows. We find that while the central clumps in Haro 14 are Hii-region complexes, the morphology and line ratios of the whole low-surface-brightness component are not compatible with star formation photoionization. In the spatially resolved emission-line-ratio diagnostic diagrams, spaxels above the maximum starburst line form the majority (∼75% and ∼50% in the diagnostic diagrams involving [O i] and [S ii] respectively). Moreover, our findings suggest that more than one alternative mechanism is ionizing the outer galaxy regions. The properties of the diffiuse component are consistent with ionization by diluted radiation and the large filaments and shells are most probably shocked areas at the edge of bubbles. The mechanism responsible for the ionization of the faint individual clumps observed in the galaxy periphery is more difficult to assess. These clumps could be the shocked debris of fragmented shells or regions where star formation is proceeding under extreme conditions
New insights to the photometric structure of Blue Compact Dwarf Galaxies from deep Near-Infrared studies: II. The sample of northern BCDs
This paper is part of a series of publications which present a systematic
study of Blue Compact Dwarf (BCD) Galaxies in the Near Infrared (NIR). Compared
to the visible light, NIR data allow a better separation of the starburst
emission from the light distribution of the old stellar low-surface brightness
(LSB) host galaxy. We analyze deep NIR broad band images of a sample of 11
BCDs, observed with the Calar Alto 3.6m telescope. This work enlarges the
samples presented in preceding papers of this study (Noeske et al. 2003, Cairos
et al. 2003) by BCDs of the most common morphological type, displaying a
regular elliptical LSB host galaxy. The data presented here allow the detection
and quantitative study of the extended stellar LSB host galaxy in all sample
BCDs. The NIR surface brightness profiles (SBPs) of the LSB host galaxies agree
at large galactocentric radii with those from optical studies, showing also an
exponential intensity decrease and compatible scale lengths. Similar to Noeske
et al. (2003), we find centrally flattening exponential (type V) SBPs of the
host galaxy for several BCDs. Such SBPs remain mostly undetected in optical
bands, due to the comparatively stronger starburst emission at these
wavelengths. We apply a modified exponential distribution to decompose and
quantitatively analyze SBPs of LSB hosts with a type V intensity distribution.
We present the results of the surface photometry and the decomposition of SBPs,
and discuss individual objects with respect to morphological details of their
star-forming regions.Comment: 18 pages, 11 figures; accepted for publication in Astronomy &
Astrophysics; postscript file with full resolution images available at
http://www.ucolick.org/~kai/PUB/noeske_nirbcds_2.ps.g
The Host in Blue Compact Galaxies: Structural Properties and Scaling Relations
We have characterized the underlying stellar host in a sample of 28 blue
compact galaxies (BCGs), by fitting their 2D light distributions. Their
structural parameters were related with galaxy properties such as colours and
gas content. These properties were also compared with those of other galaxy
types. All the BCG hosts but one show low Sersic indexes (0.5 < n < 2), with
mean effective radius =1.110.74 kpc, and mean surface
brightness = 22.590.68 mag arcsec. Host effective
radii scale linearly with their luminosity, while n and do not.
In addition, host colours and structural parameters are not linearly
correlated. Overall,the flux enhancement caused by the starburst is about 0.8
mag while their B-R colours decrease by about 0.2 mag. Galaxies with more
luminous and extended hosts show larger and luminous starburst components. BCG
hosts show B-R=0.950.26 in median. Overall, BCG hosts are more compact (by
a factor ~2) and have higher central surface brightnesses (by about ~2 mag)
than dIs and most dEs. BCG hosts and dIs are indistinguishable in the B-band
Tully-Fisher relation (TFR). We found that about 50-60 % of the galaxies are
more underluminous than those late-type discs with the same circular velocity.
This feature is more important when luminosities are converted into stellar
masses, while it tends to diminish when the HI gas mass is added. Deviations
among host masses for a given circular velocity from the stellar TFR correlate
with their HI mass-to-luminosity ratio, whereas deviations from the gas+stellar
TFR, do not. Overall, our findings suggest that the baryonic mass in BCGs tends
to normal values but BCGs tend to be inefficient producing stars, especially
toward the low-mass, gas-rich and bluest hosts, in a similar way to dIs.Comment: 25 pages, 11 figures (low-res). Accepted for publication in A&A.
Added reference. Language revisio
Revealing the Jet Structure of GRB 030329 with High Resolution Multicolor Photometry
We present multicolor optical observations of the nearby (z=0.1685) GRB
030329 obtained with the same instrumentation over a time period of 6 hours for
a total of an unprecedented 475 quasi-simultaneous BVR observations. The
achromatic steepening in the optical, which occurs at t~0.7 days, provides
evidence for a dynamic transition of the source, and can be most readily
explained by models in which the GRB ejecta are collimated into a jet. Since
the current state-of-the-art modeling of GRB jets is still flawed with
uncertainties, we use these data to critically assess some classes of models
that have been proposed in the literature. The data, especially the smooth
decline rate seen in the optical afterglow, are consistent with a model in
which GRB 030329 was a homogeneous, sharp-edged jet, viewed near its edge
interacting with a uniform external medium, or viewed near its symmetry axis
with a stratified wind-like external environment. The lack of short timescale
fluctuations in the optical afterglow flux down to the 0.5 per cent level puts
stringent constraints on possible small scale angular inhomogeneities within
the jet or fluctuations in the external density