17 research outputs found
Revisiting the Integrated Star Formation Law. I. Non-starbursting Galaxies
We use new and updated gas- and dust-corrected star formation rate (SFR) surface densities to revisit the integrated star formation law for local "quiescent" spiral, dwarf, and low surface brightness galaxies. Using UV-based SFRs with individual IR-based dust corrections, we find that "normal" spiral galaxies alone define a tight Ξ£_(H I + H2)βΞ£_(SFR) relation described by an n = 1.41^(+0.07)_(-0.07) power law with a dispersion of 0.28^(+0.02)_(-0.02) (errors reflect fitting and statistical uncertainties). The SFR surface densities are only weakly correlated with H I surface densities alone, exhibiting a stronger and roughly linear correlation with H2 surface densities, similar to what is seen in spatially resolved measurements of disks. However, many dwarf galaxies lie below the star formation law defined by spirals, suggesting a low-density threshold in the integrated star formation law. We consider alternative scaling laws that better describe both spirals and dwarfs. Our improved measurement precision also allows us to determine that much of the scatter in the star formation law is intrinsic, and we search for correlations between this intrinsic scatter and secondary physical parameters. We find that dwarf galaxies exhibit second-order correlations with the total gas fraction, stellar mass surface density, and dynamical time, which may explain much of the scatter in the star formation law. Finally, we discuss various systematic uncertainties that should be kept in mind when interpreting any study of the star formation law, particularly the X(CO) conversion factor and the diameter chosen to define the star-forming disk in a galaxy
Revisiting the Integrated Star Formation Law. Paper I: Non-Starbursting Galaxies
This research has made use of the NASA/IPAC Extragalactic
Database (NED), which is operated by the Jet
Propulsion Laboratory, California Institute of Technology,
under contract with the National Aeronautics and
Space Administration. This research was supported in
part by the STFC through a consolidated grant to the
Institute of Astronomy, University of Cambridge. M. A.
de los Reyes also acknowledges the financial support of
the Winston Churchill Foundation and the NSF Graduate
Research Fellowship Program.
The authors would like to thank the anonymous referee
for their thoughtful and constructive comments, as
well as M. Irwin, A. Saintonge, L. Hunt, and J. Wang
for their useful comments and advice. Finally, we would
like to express our deep gratitude to the staff at academic
and telescope facilities, particularly those whose
communities are excluded from the academic system,
but whose labor maintains spaces for scientific inquiry.
Software: Matplotlib (Hunter 2007), Linmix (Meyers
2015), Astropy (Astropy Collaboration et al. 2013)
Revisiting the Integrated Star Formation Law. I. Non-starbursting Galaxies
We use new and updated gas- and dust-corrected star formation rate (SFR) surface densities to revisit the integrated star formation law for local "quiescent" spiral, dwarf, and low surface brightness galaxies. Using UV-based SFRs with individual IR-based dust corrections, we find that "normal" spiral galaxies alone define a tight Ξ£_(H I + H2)βΞ£_(SFR) relation described by an n = 1.41^(+0.07)_(-0.07) power law with a dispersion of 0.28^(+0.02)_(-0.02) (errors reflect fitting and statistical uncertainties). The SFR surface densities are only weakly correlated with H I surface densities alone, exhibiting a stronger and roughly linear correlation with H2 surface densities, similar to what is seen in spatially resolved measurements of disks. However, many dwarf galaxies lie below the star formation law defined by spirals, suggesting a low-density threshold in the integrated star formation law. We consider alternative scaling laws that better describe both spirals and dwarfs. Our improved measurement precision also allows us to determine that much of the scatter in the star formation law is intrinsic, and we search for correlations between this intrinsic scatter and secondary physical parameters. We find that dwarf galaxies exhibit second-order correlations with the total gas fraction, stellar mass surface density, and dynamical time, which may explain much of the scatter in the star formation law. Finally, we discuss various systematic uncertainties that should be kept in mind when interpreting any study of the star formation law, particularly the X(CO) conversion factor and the diameter chosen to define the star-forming disk in a galaxy
The Stellar Kinematics of Void Dwarf Galaxies Using KCWI
Dwarf galaxies located in extremely under-dense cosmic voids are excellent
test-beds for disentangling the effects of large-scale environment on galaxy
formation and evolution. We present integral field spectroscopy for low-mass
galaxies () located inside (N=21) and
outside (N=9) cosmic voids using the Keck Cosmic Web Imager (KCWI). Using
measurements of stellar line-of-sight rotational velocity
and velocity dispersion , we test the tidal stirring
hypothesis, which posits that dwarf spheroidal galaxies are formed through
tidal interactions with more massive host galaxies. We measure low values of
for our sample of isolated dwarf
galaxies, and we find no trend between and
distance from a massive galaxy out to
Mpc. These suggest that dwarf galaxies can become dispersion-supported "puffy"
systems even in the absence of environmental effects like tidal interactions.
We also find indications of an upward trend between
and galaxy stellar mass, perhaps implying
that stellar disk formation depends on mass rather than environment. Although
some of our conclusions may be slightly modified by systematic effects, our
main result still holds: that isolated low-mass galaxies may form and remain as
puffy systems rather than the dynamically cold disks predicted by classical
galaxy formation theory.Comment: 19 pages including references; submitted to ApJ. Code used for
analysis and figures can be found here:
https://github.com/mdlreyes/void-dwarf-analysi