My group Research


starbursts with alma

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Some galaxies produce stars at a frenzied pace, going through the available reservoir of gas in a very short time. What is at the root of the starburst phenomenon? What drives the short timescales and high efficiencies? What controls the length of the star formation episode: gas depletion, or feedback that prevents further star formation?

This is our image of molecular gas in NGC 253, one of the nearest starbursts (Bolatto et al. 2013). It was featured in Nature as one of the 2013 images of the year.

Normal galaxies at low and high redshift

Most galaxies live rather settled lives and evolve passively, gathering gas from the “cosmic web” or minor mergers and converting it to stars. Indeed, the tightness of the relation between star formation activity and galaxy mass at different redshifts indicates this is the main mode of evolution for galaxies that are not very massive. What regulates the conversion of gas into stars in normal galaxies?

This shows our study of molecular gas in the PHIBSS sample of normal galaxies at redshifts of 1 to 3 (Tacconi et al. 2013).

The abundance of heavy elements (the metallicity) of the interstellar medium increases steadily from the earliest galaxies to present day systems. This abundance has profound effects on many processes taking place in galaxies, particularly the thermodynamics of the neutral phases and the photodissociation of the molecular phase. Many of these effects are mediated by the abundance of dust. What sets the dust-to-gas ratio in the ISM? How does it change with heavy element abundance or other galaxy parameters? How does it change within galaxies?

On the top left is our detection of FIR dust emission in one of the lowest metallicity galaxies (I Zw 18) and the measurement of its dust mass (Fisher et al. 2014). On the bottom left is our study of relation between gas and star formation in the Large Magellanic Cloud (Jameson et al. in prep.)

The ism at low metallicities

Carbon monoxide is a very abundant molecule in the ISM with low energy transitions that are excited at very low temperatures. Therefore it is used to trace the molecular hydrogen gas that makes the bulk of the molecular mass of galaxies. How good is it as a quantitative tracer of molecular mass? How does the CO-to-H2 conversion change with galaxy properties? What are the physical processes that cause these changes?

On the right is a plot from our recent ARAA review on this topic, summarizing the changes observed in very high density systems and our suggested parametrization (Bolatto et al. 2013).

Using CO emission to measure molecular masses

Katie Jameson

Rodrigo Herrera-Camus

Steven Warren

David B. Fisher

dark matter in galaxies: the central density profile

The masses of galaxies and galaxy clusters are dominated by dark matter, which makes up a fraction of all matter that is 5 times larger than normal baryons. Early dark-matter-only simulations showed that cold dark matter reaches very high densities in galaxy centers. Measurements of the distribution of dark matter provide clues to the process of galaxy formation and the relative importance of mechanisms that redistribute it within galaxies. What is the dark matter density profile in galaxy centers? How does it change with galaxy properties?

On the left is a combined CO and Ha from Simon et al. (2005). We have recently been awarded time at Palomar and CARMA to carry out similar work on a much larger sample.

understanding Far-infrared fine-structure transitions

Some of the brightest far-infrared and submillimeter-wave lines in galaxies are fine-structure transitions from the interstellar medium. They carry a wealth of information and can be studied from the ground with instruments such as ALMA for sources at medium and high redshifts. For local galaxies, many of these lines can be studied from space with Herschel or using an stratospheric observatory like SOFIA.

On the right is our work relating ionized carbon [CII] emission to the star formation rate in normal galaxies, using data from the Herschel KINGFISH project (Herrera-Camus et al. in prep.)