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Star Formation in HI-Selected Galaxies
Jessica Rosenber
George Mason University


AKARI

Arecibo

Today s Technology

Spitzer


The Next Generation

SKA

ALMA

JWST

Herschel


Questions to address by studying SF in HIselected galaxies
· What is the best way to measure SF in galaxies that, in some cases, may be metal poor · What is the SF rate density in the local universe? · How is SF distributed as a function of galaxy mass? (downsizing) · How does environment effect SF in galaxies? · How does SF efficiency vary with galaxy mass? · How does environment effect SF efficiency?


Gas Rich Galaxy Types
· HI selected surveys cover a wide range of galaxy types

· are normal spirals are irregular low surface brightness galaxies

· not detected optically mostly because they are in the Galactic plane

Salzer et al


Example Broad Band Images of ADBS Galaxies
Bright Spirals


Example Broad Band Images of ADBS Galaxies
LSB Dwarfs


Example Broad Band Images of ADBS Galaxies Is it a star or a galaxy?
The fuzzy star is just barely resolved relative to the star below it This is an ULTRA COMPACT galaxy!

?

ADBS


Not a star an ultra compact star forming dwarf galaxy!

· Emission line spectrum ·Small knot of central star formation · Not easily identi ed as a galaxy

·B · Vhelio · MB

km s


An ultra compact star forming dwarf galaxy within a large HI disk
· Intense star formation in the central region · Extended HI disk with no evidence for stars · HI is in a ring around the star formation

John Cannon et al


For HI selected surveys SF at low metallicity is important a signi cant population is low Z

Spectrum of a metal poor HII region in ADBS OH solar


Measuring Star-Formation in Star-Forming Dwarf Galaxies
· · MB · Emission line selected · Mostly low metallicity of gas rich galaxies

Lee et al 2002

Rosenberg et al. 2006


Measuring Star-Formation in Star-Forming Dwarf Galaxies

What do we measure in the optical and infrared?
stars hot dust + PAH warm dust

Mid far IR is a measure of re radiated starlight most of which comes from young star forming regions


What does the dust look like?

Red - 8.0 m Green - 4.5 m Blue - 3.6 m


Dwarf galaxies do not have SEDs well matched by templates


Infrared observations show us that even low metallicity galaxies have dust However, dust properties are different from their higher metallicity counterparts - the steep midinfrared continuua in these galaxies may imply an excess of emission from small grains

The different SEDs of low metallicity galaxies implies that we will need to take care in comparing infrared determined SFRs are different redshifts


Comparison of star formation rate calculated at di erent wavelengths
·UV higher than others an indication that dust and gas have been removed from star formation region?


Narrow Band Images of ADBS Galaxies
R Band H Narrow Band

Examples: Spirals
ADBS NGC Vel MB km s

ADBS NGC Vel MB km s


Narrow Band Images of ADBS Galaxies
R Band H Narrow Band

Examples: Dwarfs
ADBS

Vel MB

km s

ADBS

Vel MB

km s


The Star-Formation Rate Density in the Local Universe
· Determined from the HIPASS data · Should be less biased that starforming galaxy surveys · Small number of very local sources · Finds a similar answer to other work

Hannish et al. 2006


Where do we go from here?
· Ongoing HI surveys will provide the HI-selected samples from which we can address many of these questions in the local universe · Need to understand star-formation in the extreme regimes that many of the HI-selected galaxies occupy · Star-formation rate, star-formation density, and effect of environment are what current surveys allow us to address in ways that we have not be able to previously · Work on these problems is the basis for study evolution in these properties in ways that will be possible once SKA, ALMA, JWST, etc are online


All of the Original Questions Need to be Solidified
· Study the effect of metallicity and galaxy properties on measurements of SF · Determine SFR density in the local universe · Determine how SF is distributed as a function of galaxy mass? · Determine how environment effects SF in galaxies? · Determine how SF efficiency varies with galaxy mass? · Determine how environment effects SF efficiency?