Research

What is Interstellar Dust?

Interstellar dust grains are small particles (comparable to smoke particles) commonly seen in the interstellar medium of galaxies. These grains play an important role in the formation of stars (more details). Dust also absorbs light at ultraviolet to near-infrared wavelengths and this can significantly alter the appearance of stars (see image below) and galaxies. Understanding the behavoir of this absorption as a function of wavelength allows astronomers to correct for its effect and is a major focus of my research.  

Images of Barnard 68, a star forming region, at different wavelengths. This region contains a large amount of gas and dust. The dust is absorbing and scattering the light emitted from stars in the background along the line of sight. The amount of light that is blocked (absorbed) and scattered depends on wavelength, with stronger effects at bluer wavelengths than at redder wavelengths (more details). A good analogy of this effect is when the sky looks red during a bushfire/wildfire and this because smoke particles (roughly similar to interstellar dust) are better at absorbing and scattering bluer light than redder light. Galaxies contain numerous star forming regions like Barnard 68 (these often appear as spectacular dust lanes) and this can significantly affect their observed spectral energy distribution (SEDs). Image credit: ESO. 

My Research - Understanding Dust Attenuation in Galaxies

One of the largest uncertainties in our ability to characterize the physical properties of galaxies (e.g., star formation rates, stellar mass), both nearby and very distant, stems from our limited understanding of the influence that dust has on the light of galaxies at different wavelengths (i.e., their SEDs; see image below, left). In particular, I am interested in characterizing the evolution of dust attenuation at different wavelengths as a function of cosmic time (often expressed as a redshift, z; see image below, right). The goal of my research is to improve our ability to correct for the effects of dust on galaxy SEDs over a wide range of redshift. Obtaining accurate galaxy properties, free from the uncertainties of dust, is critical to improving upon our current paradigm of galaxy evolution.

Above: The intrinsic spectral energy distribution (SED) of a star-forming galaxy (blue curve) experiences attenuation from dust that reduces the observed light at UV to near-IR wavelengths. This energy is reradiated by dust at mid-IR to sub-mm wavelengths (red curve). Understanding the wavelength-dependent nature of this attenuation is crucial for accurately determining various galaxy properties. Figure modified from Conroy (2013).

Above: Comparison between dust attenuation curves (colored lines) as a function of cosmic time (redshift, z). Dust curves appear to have steeper slopes (S) at higher redshifts, however the details behind this evolution are poorly understood. Local dust extinction curves are also shown for reference (gray lines). Figure from Battisti et al. (2022).

Collaborations

MAGPHYS - Modeling the Emission of Galaxies

Above: Example of an SED fit to UV through sub-mm data (red squares) for a galaxy using MAGPHYS+photo-z (Battisti et al. 2019). The black line is the best-fit model and the blue line is the prediction for the unattenuated stellar continuum.

I am also interested in finding the best way to take observations of galaxies at various wavelengths (i.e., the SED) and transforming them into the physical properties necessary to understand galaxy evolution. I work with Elisabete da Cunha on implementing various improvements into the SED-fitting code MAGPHYS (da Cunha et al 2008, 2015; Battisti et al. 2019, 2020). This user-friendly code derives key physical properties of galaxies from their ultraviolet-to-radio observations

WFC3 Infrared Spectroscopic Parallel (WISP) 

I leding the release of ancillary photometric data and emission line products for WISP (Battisti et al. 2024). These data are publicly available through the MAST archive. In Battisti et al. (2022), we used hundreds of galaxies the HST grism surveys WISP and 3D-HST to examine the behavior of dust attenuation at z ~ 1. This project serves as a stepping stone for similar studies using grism surveys from JWST, Euclid, and Roman. In particular, I am part of the JWST PASSAGE and POPPIES surveys that started in 2023 and are successors to the WISP survey that are going a factor of 10x deeper in sensitivity than WISP.  

Right: The WISP survey provides measurements of Hα and Hβ (from Atek et al. 2010) for galaxies at 0.7<z<1.5, which is a useful diagnostic of dust attenuation.

Middle Ages Galaxy Properties with Integral Field Spectroscopy (MAGPI)

I lead the emission line working group and development of emission line data products for the survey. Previous work on dust attenuation has mainly focused on integrated measurements of galaxies. I am currently working on a project using MAGPI to study spatially-resolved dust attenuation in galaxies at z~0.3.

Right: The MAGPI survey provides spatially-resolved measurements of emission lines for galaxies up to z~1.

TYPHOON

I lead the emission line data product and ancillary photometry for the survey. The unique field-of-view of TYPHOON (orange box, below) is 100-1000x larger relative to other optical integral field spectrographs (smaller colored boxes). I am using TYPHOON to perform spatially-resolved comparisons between all baryonic components within galaxies (stars, ionised gas, molecular gas, atomic gas, and dust).

Publications


NGC4414 Image credit: NASA, ESA, W. Freedman et al., Hubble Heritage Team (AURA/STScI), SDSS; J. Schmidt.   APOD link