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The SMUDGES Survey

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Minutes of the talk on the:
SMUDGES Survey

Liese van Zee (Indiana U.)

SMUDGES = Systematic Multiwavelength Unbiased catalog of Dwarf Galaxies and Evolution of Structure.

This survey will using the 3.5 and 0.9m telescopes of the WIYN Observatory to conduct an unbiased survey for dwarf galaxies.

Science questions:

What initiates and regulates SF activity in low density, low Z environments.
What percentage of low mass galaxies experience starburst (SB) episodes?
- What is the duty cycle for such SB systems?
Are SB and dwarf Irregular separate phases in the life of a system?
- The answer is probably no. There are two kinds of galaxies, those that SB and those that don't.
- Need a survey that identifies both kinds?

Isolated LSBDG's exhibit a huge dynamic range of star formation activity so what's needed is an unbiased catalog of dIs.

Key goals:

Determine the fraction of dwarfs that go through SB phase
Investigate SF triggering mechanisms and measure the SF duty cycle
Calculate the LF
Look for differences between bursting and non-bursting dwarfs

Survey requirements:

The SMUDGES Survey will cover 134 square degrees of imaging in in BVI, plus optical spectroscopy of about 13,000 galaxies and H-alpha imaging for thousands of galaxies.
Need multicolors to discriminate via their colors, normal dwarfs from SB dwarfs. This discrimination is done by looking for color gradients which are not seen in most normal dwarfs, but are evident in SB systems. In starbursts, one sees an inverse color gradient relative to normal spirals, bluer in the center.
Also, some dwarfs have same compact scale lengths as SB's and a color gradient, but no evidence of on-going enhanced SF (e.g. no SB). These might be post-starburst systems. Hence, we can discriminate 3 categories
- starburst
- post starburst
- never starburst

Survey design

DGs are small and faint with diameters of ~0.5 kpc and absolute magnitudes M_B ~ -12. At 100 Mpc, such a galaxy subtends only 1 arcsec and has an apparent magnitude m_B ~ +23. Therefore, you need to survey a large area to have a sufficient volume to find enough dwarfs. So this criterion is similar to that for HI surveys, and likewise one must worry about beam filling factors.

First results: discovery of a dE in the field

In one of our first runs, we have identified a small dE galaxy characterized by m_B = 21, (B-I) = 1.8, z = 0.003, M_B = -9.4. This is a very small galaxy. It is isolated, no (known) nearby neighbors (yet), though we still need redshifts for some of the HSB objects in this field.

From SMUDGES, we hope to learn about the role of environment in the evolution of dwarf galaxies and, in particular, how dE's are formed in isolated regions.

Project design

To conduct such a blind, unbiased survey, SMUDGES must cover a large area.
Modest integration times are necessary to find low mass (faint) galaxies.

Determination of both the HI mass function and the optical LF function, and how those two might be related, is really important.

Questions/Discussion

Peppo G:	What is typical the HI mass and distribution of IZw18 and U2684?
Liese	Both have about 10⁸ solar masses of HI. 1Zw18 is an extensive HI object with a "tail" and a companion which HI extends very far. UGC 2684 is a more typical dwarf. HI goes out twice as far as optical.
Judith I.	Is the ALFALFA survey as described sufficient to detect dwarfs?
Liese	You want to be sensitve down to 10⁶ solar masses in the nearest volume, so 1 min or less with Arecibo achieves that out to 20 Mpc.
Wim vD	10⁶ solar masses at Virgo is quite a long integration.
Liese	But increasing the area is better so we have to compromise.
Riccardo G.	Are there any objects with total HI masses of 10⁶ solar masses which have been discovered previously?
Liese	In the Local Group, the dwarfs go down to 10⁷ solar masses. Low mass galaxies are very rare, so we need to cover a lot of area.