About Gabriela

I am a PhD researcher in Astronomy at the Leiden Observatory. My work focuses on understanding the physics of galaxies and accreting black-holes in the early Universe. Some questions I would like to answer are: How do galaxies and their nuclear black-holes grow? What are the main properties regulating the evolution of galaxies?

The information travelling towards us from galaxies and their nuclei is fascinating and complex. They emit light from all wavelengths across the electromagnetic spectrum, and even gravitational waves have been recently detected that originate in merging black-holes!

The approach of my research is thus multiwavelength, meaning that I use observations taken by telescopes across the spectrum, including the low-frequency radio (LOFAR), sub-millimeter (ALMA), infra-red (Herschel/Spitzer/WISE), optical (HST), and X-rays (XMM/Chandra) frequencies.
I am particularly interested in the potential of new spectral windows, such as those opened by ALMA and LOFAR, to unveil paths of galaxy evolution.

At the Leiden observatory, I am part of the submillimeter galaxies group led by Dr. Jacqueline Hodge and the radio astronomy group led by Prof. Huub Rottgering. Previously, I was part of the ENIGMA group at the Max Planck Institute for Astronomy (Germany), led by Joseph Hennawi(UCSB).

Research interests

In this word-cloud you can see the most frequenty used keywords in my first-author publications.

My current research focusses in understanding the most luminous phases of galaxy evolution in the early Universe. Here you can find some selected results:
The Spectral Energy Distributions (SEDs) of AGN and star-forming galaxies

A multiwavelength approach is crucial to achieve a complete and unbiased physical characterization of galaxies and AGN.
In CR+16 we presented AGNfitter, a probabilistic tool to fit SEDs of galaxies and AGN from a Bayesian approach, thus ensuring a robust handling of uncertainties in the parameters.

AGNfitter is publicily available and can be downloaded from here.
The Spectral Energy Distributions (SEDs) of AGN and star-forming galaxies

A multiwavelength approach is crucial to achieve a complete and unbiased physical characterization of galaxies and AGN.
In CR+16 we presented AGNfitter, a probabilistic tool to fit SEDs of galaxies and AGN from a Bayesian approach, thus ensuring a robust handling of uncertainties in the parameters.

AGNfitter is publicily available and can be downloaded from here.
The low-frequency radio as a SFR tracer

The radio regime is a reliable dust-unbiased tracer of star-formation rate (SFR) due to its tight correlation with the IR (infrared-radio correlation, IRC). While radio observations at frequencies higher than 1.4 GHz have been extensively used for SFR studies, this is not the case for the low frequencies. Low-frequency observations, however, are very promising since they can go deeper than high-frequencies due to the negative power-law shape of the radio SED.

In CR+17, we calibrate the low-frequency radio (150 MHz) as an SFR tracer for the first time. The LOFAR Bootes field, as one of the deepest radio galaxies surveys to-date, allowed us to characterize the IRC to high-redshifts (0<z<2.5). We found that the infrared-radio correlation is not constant as a function of redshift, but decreases following the formula on the right.

The low-frequency radio as a SFR tracer

The radio regime is a reliable dust-unbiased tracer of star-formation rate (SFR) due to its tight correlation with the IR (infrared-radio correlation, IRC). While radio observations at frequencies higher than 1.4 GHz have been extensively used for SFR studies, this is not the case for the low frequencies. Low-frequency observations, however, are very promising since they can go deeper than high-frequencies due to the negative power-law shape of the radio SED.

In CR+17, we calibrate the low-frequency radio (150 MHz) as an SFR tracer for the first time. The LOFAR Bootes field, as one of the deepest radio galaxies surveys to-date, allowed us to characterize the IRC to high-redshifts (0<z<2.5). We found that the infrared-radio correlation is not constant as a function of redshift, but decreases following the formula on the right.

The shape of the radio continuum of galaxies and AGN

In CR+17 we presented the first high-redshift galaxy and AGN study of a LOFAR survey (Bootes), one of the deepest surveys to-date. We constructed for the first time the low-to-high frequency radio SED for a statistical sample of high-z star-forming galaxies and AGN (0<z<2.5), using four different radio interferometers: LOFAR, VLA, WSRT and GMRT.

We found a significant difference in the shape of the radio continuum between AGN and star-forming galaxies. This result suggests two possible scenarios: a) instrinsic physical differences in the production of radio emission of these both populations or b) significat absorption at low frequencies in star-forming regions.
The shape of the radio continuum of galaxies and AGN

In CR+17 we presented the first high-redshift galaxy and AGN study of a LOFAR survey (Bootes), one of the deepest surveys to-date. We constructed for the first time the low-to-high frequency radio SED for a statistical sample of high-z star-forming galaxies and AGN (0<z<2.5), using four different radio interferometers: LOFAR, VLA, WSRT and GMRT.

We found a significant difference in the shape of the radio continuum between AGN and star-forming galaxies. This result suggests two possible scenarios: a) instrinsic physical differences in the production of radio emission of these both populations or b) significat absorption at low frequencies in star-forming regions.
Multi-wavelength + high-resolution:
Off-set distributions of stars, gas and dust


In CR+18, we combined ALMA and HST observations of four submillimeter galaxies to study the distributions of the molecular gas emission (CO line, lower-left panel and white countours in the righ panel) and the optical/NIR stellar emission (background image in right panel).

We find that in most cases these components are significantly off-set, suggesting these are originated in different physical regions!
Most strikingly, we also find singificant off-sets when comparing the stellar to the dust continuum emission. This, together with similar finding of other high-res observations, has implications against energy balance assumptions in integrated SED fitting.

Multi-wavelength + high-resolution:
Off-set distributions of stars, gas and dust


In CR+18, we combined ALMA and HST observations of four submillimeter galaxies to study the distributions of the molecular gas emission (CO line, lower-left panel and white countours in the righ panel) and the optical/NIR stellar emission (background image in right panel).

We find that in most cases these components are significantly off-set, suggesting these are originated in different physical regions!
Most strikingly, we also find singificant off-sets when comparing the stellar to the dust continuum emission. This, together with similar finding of other high-res observations, has implications against energy balance assumptions in integrated SED fitting.

Multi-wavelength + high-resolution:
Extended gas and compact dust


Using larger samples of submillimeter galaxies (SMGs) we apply a statistical approach through stacking to study the differences in the extents of gas and dust, as shown by their radial profile.

We find that the average extent of the CO emission in SMGs is more than twice as large as the dust continuum emission.

We investigate the origin of this difference by modelling both the gas and dust emission consistently through radiative transfer. We found that this apparent size difference can be explained by temperature and optical depth gradients alone, and does not necessarily imply different physical sizes.
Multi-wavelength + high-resolution:
Extended gas and compact dust


Using larger samples of submillimeter galaxies (SMGs) we apply a statistical approach through stacking to study the differences in the extents of gas and dust, as shown by their radial profile.

We find that the average extent of the CO emission in SMGs is more than twice as large as the dust continuum emission.

We investigate the origin of this difference by modelling both the gas and dust emission consistently through radiative transfer. We found that this apparent size difference can be explained by temperature and optical depth gradients alone, and does not necessarily imply different physical sizes.

First and second author publications

    img ORCID ID : 0000-0003-0085-6346

  • AGNfitter: A Bayesian MCMC Approach to Fitting Spectral Energy Distributions of AGNs
    Calistro-Rivera et al. (2016) - ApJ,833,98C

  • The LOFAR window on star-forming galaxies and AGNs - curved radio SEDs and IR-radio correlation at 0<z<2.5
    Calistro-Rivera et al. (2017) - MNRAS.469.3468C

  • LOFAR-Boötes: properties of high- and low-excitation radio galaxies at 0.5 < z< 2.0
    Williams, Calistro-Rivera et al. (2018) - MNRAS, 475, 3429W

  • Resolving the ISM at the Peak of Cosmic Star Formation with ALMA: The Distribution of CO and Dust Continuum in z ~ 2.5 Submillimeter Galaxies
    Calistro-Rivera et al. (2018) - ApJ,863,56C

  • The Distribution of [CII], CO and Dust Continuum in z ~ 3 Submillimeter Galaxies
    Rybak, Calistro-Rivera et al. (2018) - in prep

  • A multiwavelenght census of growing black-holes in dusty star-forming galaxies
    Calistro-Rivera et al. (2018) - in prep

Other publications: 14 refereed and non-refereed.
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Contributed and invited talks at conferences and workshops

    2014

  • Southern Cross Conference 2014 ’Powerful AGN’ (contributed talk) Port Douglas - Australia

    2015

  • Galaxy studies in the mid-infrared - Symposium EWASS15 (contributed talk) Tenerife,Spain

  • The infrared-radio correlation - Special Session EWASS15 (contributed talk) Tenerife,Spain

  • LOFAR science conference (contributed talk) Leiden, The Netherlands

    2016

  • Cosmic Dawn of Galaxy Formation: Linking observations and theory (contributed talk) Paris, France video gif

  • AGN: What’s in a name? - ESO workshop (contributed talk) Garching - Germany

  • Latinamerican Regional IAU Meeting LARIM (contributed talk) Cartagena - Colombia

    2017

  • Distant Galaxies from the Far South (contributed talk) Bariloche, Argentina

    2018

  • The ISM as a window onto galaxy evolution - Symposium EWASS18 (contributed talk) Liverpool, UK

  • CANDELS: The art of measuring physical parameters in galaxies (invited review talk) Riverside, US

  • Lorentz Center workshop on Photometric Redshifts(invited review talk) Leiden - The Netherlands img

  • IAU Symposium 341: Challenges in Panchromatic Galaxy Modelling (contributed talk) Osaka - Japan img

Teaching

Supervision of students:

  • 2017 : Supervision of the Bachelor Thesis of Auke Bruinsman.
    Topic: radio jets of a nearby AGN.

  • 2018 : Supervision of the Bachelor Thesis of Danker Roozemond.
    Topic: The AGN contribution to sub-millimeter galaxies.


    Courses

  • 2016 - 2017: Galaxies: Structure and Dynamics
    Teaching Assistant of Rychard Bouwens' lecture on Galaxies at Leiden Observatory in the Fall 2016.

  • 2013 - 2014: Physics Laboratory
    Tutor of the Physics laboratory for Bachelor students at Heidelberg University. Topic: Electrodynamics.

Short Biography

  • Nov 2014 - 2018: Ph.D. researcher in Astronomy (Leiden Observatory, the Netherlands)
    Thesis: Colours of the extreme Universe
    Supervisor: Dr. Jacqueline Hodge, Prof. Huub Röttgering

  • June - Sept 2014: Short-term Research Project (MPIA, Germany)
    Project: The origin of obscuration in Dust-Obscured Galaxies
    Supervisor: Dr. Joseph Hennawi

  • 2012 - May 2014: M.Sc. in Physics (Heidelberg University / MPIA, Germany)
    Thesis: Classification of Obscured AGN through SED-fitting
    Supervisor: Dr. Joseph Hennawi, Dr. Elisabeta Lusso

  • 2008 - 2011:    B.Sc. in Physics (Heidelberg University / Institute for Theoretical Astrophysics,Germany)
    Thesis: The Lensed Temperature Anisotropy of the CMB
    Supervisor: Prof. Matthias Bartelmann

Lima, Peru

I grew up in Lima, the capital of Perú. Although Perú is predominantly known as an andean country, Lima is a coast city and the multifaceted home of around ten million people. Lately Lima has become very popular in the international comunity as a culinary paradise. Friendly advice: look for the closest Peruvian restaurant to your home, it's delicious!

Here, my school education took place mainly in the Peruvian-German School Alexander von Humboldt.

Heidelberg, Germany

My undergraduate alma-mater is the University of Heidelberg, located in a beautiful city in the south of Germany of the same name.

Here, I completed the Bachelor and Master Studies in Physics, as a DAAD scholarship holder.

My research career started at the Max Plack Institute for Astronomy (MPIA), where I worked on AGN and SED-fitting. Since this period I have worked in collaboration with Joseph Hennawi (UCSB), Elisabeta Lusso (Durham Universtiy) and David Hogg (Flatiron Institute/NYU/MPIA).

Leiden, the Netherlands

Currently I'm a PhD candidate at Leiden Observatory, in the Netherlands.

Here I am part of the sub-mm astronomy group, led by Jacqueline Hodge.

I am also part of the radio astronomy group, lead by Huub Rottgering. During my PhD I worked as well in close collaboration with Prof. Ian Smail (Durham University) and Prof. Martin Hardcastle (University of Hertfordshire).




A PDF of my CV can be found here. img

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