Recent Research

Star Formation at z=8

In a paper we published in ApJ Letters, Searching for Star Formation Beyond Reionization, Romeel Dave, J.-D. Smith, Casey Papovich, Lars Hernquist, Volker Springel, and I use the cosmological hydrodynamic simulations of Springel & Hernquist (2003) to argue that star formation at z = 8 may be detectable with present-day technology. The discovery of these objects would open whole new fields of study into the nature of the reionization and the star formation and chemical enrichment history of the universe.

We were awarded a total of 128 hours of time on the Gemini 8-meter telescope on Mauna Kea in Hawai'i, in semesters 2004A and 2005A, to search for these objects with the NIRI near-infrared imager. In 2004A, poor weather prevented us from obtaining the data, although we verified that the custom-made narrow-band filter designed by J.-D. Smith is working extremely well and that it provides a low-background window to the distant universe. In 2005A, we will image the Hubble deep field to search for Lyman alpha emission at z=8.227.

The Nature of Luminous Compact Blue Galaxies at Intermediate Redshift: Possible Links to the Formation of Galactic Bulges

Liese van Zee and I used the VLA to explore the properties of some outliers to the Tully-Fisher relation among galaxies in pairs and found that the emission-line regions of these galaxies are centralized and not spatially extended. Thus, the kinematic linewidths do not reflect the full gravitational potentials of the galaxies. We show the VLA data and explore the links between these local blue compact galaxies and intermediate-redshift compact galaxies in Possible Local Spiral Counterparts to Compact Blue Galaxies at Intermediate Redshift.

At present, I am analyzing both deep ground-based images of compact narrow emission line galaxies (CNELGs) and WFPC2 images of compact galaxies at intermediate redshift to determine the intrinsic shapes of these luminous compact objects. We are exploring the possibility that a large fraction of them are actually spiral bulges in formation.

In addition, Liese van Zee and I are using the WIYN 3.6-meter telescope on Kitt Peak and the 1.8-meter Lennon Telescope (VATT) on Mt. Graham to image over 1000 square arcminutes of sky. With deep exposures and the typically excellent seeing of the WIYN telescope (frequently sub-half-arcsecond in I), we plan to use photometric redshifts and detailed morphological information to measure the rate of in situ late-type bulge formation as a function of redshift for 0.4 < z < 1. We have an upcoming Keck run to obtain spectra of luminous compact galaxies identified in the WIYN survey.

The Merger Rate, Dark Matter Simulations, and Interacting Galaxies

As part of a number of new collaborations coming out of the Cosmology Group at UC Irvine, James Bullock and I, along with graduate students Joel Berrier and Heather Guenther, are beginning a comprehensive study of the merger rate and galaxy interactions using cosmological simulations and data in the nearby and distant universe. This work will build on my previous studies of galaxy pairs and galaxy interactions in the local universe.

Statistical Studies of Interacting Galaxies

In an ApJ article, Tidally-Triggered Star Formation in Close Pairs of Galaxies, Margaret Geller, Scott Kenyon, and I explore the match between star formation timescales and dynamical timescales in 502 galaxies in pairs. We have verified the correlations between the star-forming properties of interacting galaxies and their observable orbital parameters with an additional 200 paired galaxies; a subsequent independent study by Lambas et al. of the 2dF survey pairs reveals the same trends.

In a follow-up study, The Tully-Fisher Relation as a Measure of Luminosity Evolution: A Low-Redshift Baseline for Evolving Galaxies, we explore the ability of close galaxy-galaxy passes to trigger evolution and the effects of tidal distortion on the Tully-Fisher properties of galaxies. Sheila Kannappan and I continue the Tully-Fisher study in Tools for Identifying Spurious Luminosity Offsets in Tully-Fisher Studies: Application at Low Redshift and Implications for High Redshift

We explore the typical strengths and ages of bursts of star formation triggered by interaction with a large sample in Tidally-Triggered Star Formation in Close Pairs of Galaxies 2: Constraints on Burst Strengths and Ages. A LaTeX file with the full data table (Table 1) is available here . A second version with B-band absolute magnitudes added in a column immediately following the R-band absolute magnitudes is available here . In collaboration with S. Kannappan and R. Jansen, I also explore the relative frequency of galaxies with blue centers in the pairs survey and the Nearby Field Galaxy Survey in Forming Young Bulges within Existing Disks: Statistical Evidence for External Drivers.

My collaborators and I are currently extending these studies of the aggregate effects of interactions in the local universe in several ways, including:

  • a spectroscopic and imaging study, in collaboration with Margaret Geller and Deborah Freedman Woods at the Smithosonian Astrophysical Observatory, of minor mergers based on a search for satellites around all galaxies in the updated version of the CfA2 redshift survey; the complete study now includes over 1300 galaxies,

  • UBVRJHK imaging, in collaboration with Margaret Geller, Scott Kenyon, and Heather Geunther (UC Irvine), of over 50 of the pairs of galaxies with strong triggered star formation; the extensive wavelength coverage is necessary to constrain the old (pre-existing) and young stellar populations separately,

  • a narrow-band imaging study of galaxies with blue centers and the possible interpretation of these objects as bulges in formation, in collaboration with R. Jansen.

    Ultra-Faint Dwarf Populations Around External Galaxies: the Search for New Local Groups

    In collaboration with R. Dave, L. van Zee, J.-D. Smith, J. Fulbright, and P. Stetson, I am searching for dwarf satellites around external spiral galaxies to extremely faint magnitude limits (MR = -9). The goal of the project is to measure differential counts of faint dwarf galaxies around both early and late-type spiral galaxies without the use of a priori assumptions about the structural parameters of dwarfs to separate them from the background counts.

    We observed 4 nearby spiral galaxies with the Mosaic camera on the CTIO 4-meter telescope; we now have time on the new IMACS spectrograph at the Magellan 6.5-meter telescope to measure redshifts of faint galaxies in the environments of these spirals.

    The SMUDGES Survey and the Existence of Field Dwarf Ellipticals

    In collaboration with L. van Zee, we are using the MMT to search for field dwarf ellipticals in her blind dwarf survey, the SMUDGES survey. The existence of isolated dwarf ellipticals would invalidate models of their formation that involve tidal or ram pressure stripping. The ultimate goal of the SMUDGES survey is to make the first unbiased measurements of the luminosity functions of different types of dwarf galaxies to deep surface brightness limits.