123 research outputs found
Mapping Lyman Continuum escape in Tololo 1247-232
Low redshift, spatially resolved Lyman continuum (LyC) emitters allow us to
clarify the processes for LyC escape from these starburst galaxies. We use
Hubble Space Telescope (HST) WFC3 and ACS imaging of the confirmed low-redshift
LyC emitter Tol 1247-232 to study the ionization structure of the gas and its
relation to the ionizing star clusters. We perform ionization parameter mapping
(IPM) using [O III]4959, 5007 and [O II]3727 imaging as the high- and
low-ionization tracers, revealing broad, large-scale, optically thin regions
originating from the center, and reaching the outskirts of the galaxy,
consistent with LyC escape. We carry out stellar population synthesis modeling
of the 26 brightest clusters using our HST photometry. Combining these data
with the nebular photometry, we find a global LyC escape fraction of f_esc =
0.12, with uncertainties also consistent with zero escape and with all measured
f_esc values for this galaxy. Our analysis suggests that, similar to other
candidate LyC emitters, a two-stage starburst has taken place in this galaxy,
with a 12 Myr old, massive, central cluster likely having pre-cleared regions
in and around the center, and the second generation of 2 - 4 Myr old clusters
dominating the current ionization, including some escape from the galaxy.Comment: Accepted for publication in Ap
The effect of diffuse background on the spatially-resolved Schmidt relation in nearby spiral galaxies
The global Schmidt law of star formation provides a power-law relation
between the surface densities of star-formation rate (SFR) and gas, and
successfully explains plausible scenarios of galaxy formation and evolution.
However, star formation being a multi-scale process, requires
spatially-resolved analysis for a better understanding of the physics of star
formation. It has been shown that the removal of a diffuse background from SFR
tracers, such as H, far-ultraviolet (FUV), infrared, leads to an
increase in the slope of the sub-galactic Schmidt relation. We reinvestigate
the local Schmidt relations in nine nearby spiral galaxies taking into account
the effect of inclusion and removal of diffuse background in SFR tracers as
well as in the atomic gas.We used multiwavelength data obtained as part of the
surveys such as SINGS, KINGFISH, THINGS, and HERACLES. Making use of a novel
split of the overall light distribution as a function of spatial scale, we
subtracted the diffuse background in the SFR tracers as well as the atomic gas.
Using aperture photometry, we study the Schmidt relations on background
subtracted and unsubtracted data at physical scales varying between 0.5--2 kpc.
The fraction of diffuse background varies from galaxy to galaxy and accounts to
34 % in H, 43 % in FUV, 37 % in 24 m, and
75\% in H I on average. We find that the inclusion of diffuse background
in SFR tracers leads to a linear molecular gas Schmidt relation and a bimodal
total gas Schmidt relation. However, the removal of diffuse background in SFR
tracers leads to a super-linear molecular gas Schmidt relation. A further
removal of the diffuse background from atomic gas results in a slope 1.4
0.1, which agrees with dynamical models of star formation accounting for
flaring effects in the outer regions of galaxies.Comment: 33 pages, 25 figures, 6 tables, accepted for publication in A&
Testing metallicity indicators at z~1.4 with the gravitationally lensed galaxy CASSOWARY 20
We present X-shooter observations of CASSOWARY 20 (CSWA 20), a star-forming
(SFR ~6 Msol/yr) galaxy at z=1.433, magnified by a factor of 11.5 by the
gravitational lensing produced by a massive foreground galaxy at z=0.741. We
analysed the integrated physical properties of the HII regions of CSWA 20 using
temperature- and density-sensitive emission lines. We find the abundance of
oxygen to be ~1/7 of solar, while carbon is ~50 times less abundant than in the
Sun. The unusually low C/O ratio may be an indication of a particularly rapid
timescale of chemical enrichment. The wide wavelength coverage of X-shooter
gives us access to five different methods for determining the metallicity of
CSWA 20, three based on emission lines from HII regions and two on absorption
features formed in the atmospheres of massive stars. All five estimates are in
agreement, within the factor of ~2 uncertainty of each method. The interstellar
medium of CSWA 20 only partially covers the star-forming region as viewed from
our direction; in particular, absorption lines from neutrals and first ions are
exceptionally weak. We find evidence for large-scale outflows of the
interstellar medium (ISM) with speeds of up 750 km/s, similar to the values
measured in other high-z galaxies sustaining much higher rates of star
formation.Comment: 18 pages, 11 figures, accepted for publication in MNRA
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