H II Regions in Dwarf Irregular Galaxies S. Holmes Dept. of Physics & Astronomy College of Charleston Advisors: P. Massey (Lowell Obs.), K. Olsen (CTIO), C. Smith (CTIO), L. Penny (C of C)

The Galaxies in Question: The 3 Dwarfs (In the Local Group) NGC 6822 WLM Phoenix

Some Particulars of these Dwarves NGC 6822: Many previous studies done (Hodge 1988, 1989) WLM: limited studies Phoenix: no H II studies   Irregular Galaxies   Local Group * * “barred dwarf”, V magnitude = * * DDO 221, a.k.a. Wolf-Lundmark-Melotte (1926) * * V magnitude = * * 1976 * * No evidence of HII emission? * * V magnitude =

Galaxies & Galactic Morphology Evolution Types Significance: How do H II Regions relate? Spiral, Elliptical, Irregular... What is an H II Region?...

A Tuning Fork Diagram

O & B stars ( K)  What an H II Region is... Ionized hydrogen gas (H II) (unlike H I -- neutral hydrogen) ergs sec -1 UV flux Discharged photons & the need to be at n = 1 Balmer transition, n = 3, n = 4  Visible

Discharged photons & the need to be at n = 1 Visible: 4000 Å Å Balmer transition, n = 3, n = 4 ; 6530 Å H II detection: H  filter (6510 Å Å)

* Proximity * Varying morphologies The Local Group (¿ Que es ?) * ~40 member galaxies Milky Way, Andromeda (M31) dominate..."Why study them?"

You are looking from above…. The Milky Way is at the center

The DATA Cerro Tololo Inter-American Observatory Part of the Local Group Survey project The Team Phil Massey, Lowell Observatory Paul Hodge, University of Washington Shay Holmes, College of Charleston George Jacoby, WIYN Nichole King, Space Telescope Science Institute Knut Olsen, CTIO/NOAO Abhijit Saha, KPNO/NOAO Chris Smith, CTIO/NOAO

The DATA Wide field, MOSAIC CCD camera 8000 x 8000 pixels 2 Special  Limitations = Incompleteness For Example  Excellent choice for analysis...

Enter: The Atlas of the Andromeda Galaxy Copyright © 1981 by the University of Washington Press

Hodge’s 1989 NGC 6822

the SPLOG

Filters: How to analyze H II Regions R, 5050 ~ 8010 Å H ,6510 ~ 6615 Å

The Naked Galaxies WLMNGC 6822 Phoenix

What Science comes from these pictures? The Study of Star Formation H II as a tool Morphological Comparison Gas Dynamics

The Luminosity Function N(L) = A L a dL N = Number of regions of luminosity L A = constant L = luminosity a a = found as slope of Log (N/dL) vs. Log (L) 

Detection Discernable surface brightness limit (Kennicutt et al 1988): The By-Hand Method Precision correlated with depth and expanse of field 2 x ergs sec -1 cm -2

Regions in NGC 6822

The LUMINOSITY FUNCTION Turnover: Power-law slope fits only L > ergs sec -1

WLM

IF you’re impressed now, wait till you see Phoenix... Turnover: L > ergs sec -1

Phoenix 

Don’t laugh.

Translating the Results a 32 new regions in NGC 6822, a = ± 0.1 vs ± 0.1 Turnover: Imcompleteness vs. Inability a 35 new regions in WLM, a = ± 0.1 vs ± 0.1 TURNOVER! a Uncharted waters of Phoenix: 7 detections! a = ± 0.1 a Standard a -value = -1.7 for dwarf Irr

Acknowledgements P. Massey (Lowell Obs) D. Hunter (Lowell Obs) K. Olsen (CTIO) C. Smith (CTIO) L. Penny & R. Dukes (C of C) Mil gracias a y especialmente a,