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Register a new userHI and CO in Blue Compact Dwarf Galaxies: Haro 2 and Haro 4
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Added by
Hector Bravo-Alfaro
Publication date
2003
fields
Physics
and research's language is
English
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We present VLA HI imaging of two blue compact dwarf (BCD) galaxies, Haro 2 and Haro 4, and of the spiral galaxy Haro 26, which is projected some 22 SW of Haro 4. We also show a map of the CO(1-0) distribution of Haro 2 obtained with the OVRO millimeter array, as well as derive an upper limit for CO(2-1) emission from Haro 4 obtained with the CSO. The HI data of Haro 2 reveal that the kinematical major axis lies perpendicular to the photometric major axis, indicating that the atomic hydrogen rotates about the major axis of the galaxy. This confirms earlier indications based on CCD photometry that Haro 2 is a dust-lane dE rather than a dIrr. We propose that the present neutral and molecular ISM configuration is due to recent gas accretion or a merger. The HI distribution and dynamics of Haro 4 and the neighboring spiral Haro 26 suggest that they are currently undergoing a tidal interaction, reinforcing the notion that interactions play an important role in triggering the star formation witnessed in Blue Compact Galaxies.
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Long-slit observations of the blue compact galaxy Haro 2 have been performed to detect the Halpha emission originating in the partially ionized wind outflowing at 200 km/s, that had been previously detected with the Hubble Space Telescope. A shallow broadening of the Halpha line wings has been observed, consistent with the existence of an expanding shell. The rotation curve shows two dips at the same systemic velocity as the nucleus. At the positions of the dips the Halpha line is clearly broadened with respect to the central core. This broadening is produced by the outer layers of the expanding shell. From the position of these dips we estimate the size of the shell to be around 20 in diameter, with a corresponding kinematical age between 5 and 6 Myr. A comparison of the Halpha and Ly_alpha profiles shows that Ly_alpha is significantly broader than Halpha, with an additional emission in the red wing. We interpret this redshifted source of Ly_alpha emission as line photons backscattered by the receding part of the expanding shell. These observations outline the extremely high sensitivity of the Ly_alpha line to the structure and kinematics of the interstellar medium.
(abridged) Strongly star-forming galaxies of subsolar metallicities are typical of the high-redshift universe. Here we therefore provide accurate data for two low-z analogs, the well-known low-metallicity emission-line galaxies Haro 11 and ESO 338-IG 004. On the basis of Very Large Telescope/X-shooter spectroscopic observations in the wavelength range 3000-24000AA, we use standard direct methods to derive physical conditions and element abundances. Furthermore, we use X-shooter data together with Spitzer observations in the mid-infrared range to attempt to find hidden star formation. We derive interstellar oxygen abundances of 12 + log O/H = 8.33+/-0.01, 8.10+/-0.04, and 7.89+/-0.01 in the two HII regions B and C of Haro 11 and in ESO 338-IG 004, respectively. The observed fluxes of the hydrogen lines correspond to the theoretical recombination values after correction for extinction with a single value of the extinction coefficient C(Hbeta) across the entire wavelength range from the near-ultraviolet to the NIR and mid-infrared for each of the studied HII regions. Therefore there are no emission-line regions contributing to the line emission in the NIR range, which are hidden in the optical range. The agreement between the extinction-corrected and CLOUDY-predicted fluxes implies that a HII region model including only stellar photoionisation is able to account for the observed fluxes, in both the optical and NIR ranges. All observed spectral energy distributions (SEDs) can be reproduced quite well across the whole wavelength range by model SEDs except for Haro 11B, where there is a continuum flux excess at wavelengths >1.6mum. It is possible that one or more red supergiant stars are responsible for the NIR flux excess in Haro 11B. We find evidence of a luminous blue variable (LBV) star in Haro 11C.
We present far infrared (FIR) spectroscopy of the luminous blue compact galaxy (BCG) Haro 11 (ESO 350-IG38) obtained with the ISO Long Wavelength Spectrometer (LWS) in low resolution mode. This metal poor dwarf merger is an extremely hot IRAS source with a high [CII]158um/CO(1-0) flux ratio. We discuss the balance between dust and line cooling in the photodissociated regions (PDR), in particular the role of the [CII] line, and derive the basic properties of the PDR gas. While samples of other starburst galaxies show a correlation between the [CII]/FIR flux ratio and the IRAS f60/f100 ratio, Haro 11 deviates significantly from this relationship being brighter in [CII] than average. We propose that the relationship is caused by an increasing optical depth with increasing IRAS temperature but that the low metallicity and the extreme starburst properties of Haro 11 allow the medium to be thin despite its high f60/f100 ratio, explaining the [CII] excess. This leaves room for a more optimistic view on the possibilities to detect massive starforming mergers at high redshifts, using the [CII] line.
(Abriged) Blue compact galaxies (BCGs) are low-luminosity, metal-poor, gas-rich objects that form stars at high rates, excellent analogs to the high-redshift star-forming galaxy population. Being low-mass starbursts, they also constitute ideal laboratories for investigating star formation and massive stellar feedback. This work presents results from integral field spectroscopic observations of the BCG Haro 14 taken with the Multi Unit Spectroscopic Explorer (MUSE). The large MUSE field of view enables simultaneous observations of the starburst and the host galaxy. We built galaxy maps in continuum and in emission lines and generated synthetic VRI images, from which we produced color index maps and surface brightness profiles. We detected numerous clumps spread throughout the galaxy, both in continuum and in emission lines, and produced a catalog with their position, size, and photometry. This analysis allowed us to study the morphology and stellar populations of Haro 14 in detail. The stellar distribution shows a pronounced asymmetry; the intensity peak in continuum is not centered with respect to the stellar host but is displaced by about 500 pc southwest. At the position of the continuum peak we find a bright stellar cluster that with M$_{V}=-12.18$ appears as a strong super stellar cluster candidate. We also find a highly asymmetric, blue, but nonionizing stellar component that occupies almost the whole eastern part of the galaxy. We conclude that there are at least three different stellar populations in Haro 14: the current starburst of about 6 Myr; an intermediate-age component of between ten and several hundred million years; and a red and regular host of several gigayears. The pronounced lopsidedness in the continuum and also in the color maps, and the presence of numerous stellar clusters, are consistent with a scenario of mergers or interactions acting in Haro 14.
$^{12}CO(J=1 to 0)$ observations of 34 blue compact and star burst galaxies are presented. Although these galaxies are experiencing vigorous star formation at the current epoch, CO has been detected in only five of them. The five detections reported in this paper are all in galaxies with relatively red colours, (B-V)_0 > 0.4. The new observations, when combined with previously published data on CO in BCGs, indicate that CO luminosity decreases with absolute luminosity of BCGs. Since the absolute luminosity of a galaxy is correlated with its metallicity, these results confirm that low metallicity BCGs have low abundances of CO gas. We also show that the star formation rate determined from the $H_{beta}$ luminosity is lower than that determined from the far infrared luminosity.
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