I study the faint star-forming galaxies, known as the dwarf galaxies, at high redshifts. These galaxies play a critical role in galaxy formation and evolution, because they are the most plausible sources of ionizing photons during the reionization epoch, significantly contribute to intergalactic medium metal enrichment and maintain the ionizing background at z > 3.
1- The UV Luminosity Function at 1<z<3:
The high-redshift dwarf galaxies are inaccessible as they lay outside of the detection limits of current surveys. One powerful way to explore these faint galaxies, is to exploit the magnification of strong gravitational lensing from foreground massive clusters of galaxies and thus push the detection limits to lower luminosities. In these studies, combining deep UV imaging and high magnification from strong gravitational lensing, we identify a large sample of dwarf galaxies during the peak epoch of cosmic star formation at 1 < z < 3. From these samples, we present a robust measurement of the rest-frame UV luminosity function (LF) and its evolution at 1 < z < 3.
- Anahita Alavi, Brian Siana, Johan Richard, et al., “The Evolution of the Faint End of the UV Luminosity Function during the Peak Epoch of Star Formation (1 < z < 3)”, 2016, ApJ, 832, 56
- Anahita Alavi, Brian Siana, Johan Richard, et al., “Ultra-faint Ultraviolet Galaxies at z ~ 2 behind the Lensing Cluster A1689: The Luminosity Function, Dust Extinction, and Star Formation Rate Density”, 2014, ApJ, 780, 143
2- Dust Attenuation and Bursty Star Formation History of high-redshift Dwarf Galaxies
The UV light, which is largely emitted by young stars, provides a powerful tool to determine the star formation of galaxies at different redshifts. However, this is challenging because the UV continuum of galaxies is subject to substantial attenuation by dust. One of the most practical methods for measuring the dust attenuation in high-redshift studies is through the UV continuum slope. However, for the faint galaxies, it is more complicated due to their bursty star formation histories. We provide a comprehensive measurement of the UV spectral slopes of dwarf galaxies at 1<z<3. We show that there is a large scatter in their UV slope distribution at a given UV luminosity. Using hydro-dynamical simulations of dwarf galaxies, we demonstrate that the bursty star formation histories alone can explain this intrinsic scatter. For more details, you can see Section 4 of my Ph.D. Dissertation.
3- Lyman Continuum Scape Fraction
What are the primary sources of ionizing photons (LyC, Lyman continuum) that caused the reionization of IGM? Direct detection of Lyman continuum leaking from high-redshift galaxies (z>4) has been very challenging, mainly due to the high opacity of the IGM. Therefore, many studies have been devoted to searching Lyman continuum at intermediate redshifts, 1<z<3. I have been involved in some studies of measuring the escape fraction of LyC photons from LyC-emitting candidates at 1<z<3. This includes the first direct detection of LyC radiation from a star-forming galaxies at z=3.2.
- Vanzella, E. et al. (including Alavi), “Hubble Imaging of the Ionizing Radiation from a Star-forming Galaxy at Z=3.2 with fesc>50%”, ApJ, 825, 41
My contribution: Deep UV HST data reduction and photometry
- Vasei, K. et al.(including Alavi), “The Lyman Continuum Escape Fraction of the Cosmic Horseshoe: A Test of Indirect Estimates”, Apj, 831, 38
My contribution: Deep UV HST data reduction, Monte Carlo simulation of IGM transmission
- Siana, B. et al. (including Alavi), “A Deep Hubble Space Telescope and Keck Search for Definitive Identification of Lyman Continuum Emitters at z~3.1”, ApJ, 804, 17
My contribution: Spectroscopic observations
4- Strong Lensing Analysis of a lensing cluster MACSJ0717
In order to estimate intrinsic properties of the background lensed galaxies, we require an accurate mass model of the galaxy cluster to calculate the lensing magnification. Finding more multiply imaged systems is critical for improving the lens models, as the models are constrained by the location and the redshift of these systems. I have been involved in a strong lensing study of a galaxy cluster MACSJ0717 from the HFFs program.
- Limousin, M. et al. (including Alavi), “Strong-lensing analysis of MACS J0717.5+3745 from Hubble Frontier Fields observations: How well can the mass distribution be constrained?”, A&A, 588,99
For other contributions and a complete list of my publications you can see my ADS account.