Low Surface Brightness Science with Rubin: Unlocking LSST's Discovery Domain II

The co-chairs of the Galaxies SC Low Surface Brightness Working Group, Aaron Watkins and Sarah Brough, DM representative Lee Kelvin, and representatives from other Science Collaborations interested in low surface brightness astronomy, Ian Dell'Antonio, Annika Peter, and Yao-Yuan Mao, Peregrine McGehee, and Stephen Smartt have organized two breakout sessions on low surface brightness (LSB) astronomy with Rubin.

This, the second session, will be in-person only. But the first session will be remotely accessible. All are welcome to attend one or both sessions.


Agenda for Session 2

  • Sugata Kaviraj: "Dwarf galaxies in the LSST era: a new frontier in the study of galaxy evolution"
  • Sarah Brough: "Preparing for LSST: first intra-group light analysis in Subaru’s HSC PDR2 data"
  • Yuan-Yuan Zhang: "Characterizing the Evolution of the Intracluster Light with optical images and a tSZ cluster sample"
  • Tony Tyson: "LSB completeness requirements for LSST weak lens cosmic shear"
  • Ian Dell'Antonio: "Joint ICL and shear mapping of nearby clusters with the LoVoCCS survey on DECam"
  • Open discussion


Chair & Helper Roles 

  • note taker: Aaron Watkins
  • time keeper: Sarah Brough
  • breakout summaries slide presenter: Aaron Watkins
  • virtual moderator: Sugata Kaviraj


Abstracts for Session 2

  • Sugata Kaviraj
      • Title: "Dwarf galaxies in the LSST era: a new frontier in the study of galaxy evolution"
      • Abstract: Dwarf galaxies dominate the galaxy number density at all epochs and in all environments. However, our statistical understanding of galaxy evolution is strongly biased towards massive galaxies. This is because the surface brightness limits of past large surveys like the SDSS, which are shallow, only reveal dwarfs with anomalously high star formation rates (SFRs) outside the very local Universe. The advent of the LSST, which has a nominal SB limit of 30 mag arcsec^-2 will offer, for the first time, an unbiased sample of millions of dwarf galaxies at cosmological distances down to 10^8 MSun and out to at least z~0.5. Such samples will be game changing for our understanding of galaxy evolution. We present results using the HSC-SSP Deep survey in the COSMOS field, which reaches a similar depth to the LSST Deep-Wide-Fast survey but only over 4 degrees. We combine the COSMOS2020 value-added catalog with density measurements from the DisPerSE filament finding algorithm to perform a first study of the effect of galaxy interactions and environment (local density and distance from nodes/filaments/voids) on the evolution of around 10,000 dwarf galaxies outside the Local Group. We show that interactions enhance star formation in dwarfs (as is also observed in massive galaxies), with 10% of the dwarf star formation budget being hosted by interacting dwarfs. Red (i.e. quiescent) dwarfs show smaller distances to massive galaxies and nodes in the cosmic web than their blue counterparts. The median colour of dwarfs shows only a weak correlation with local density, except in very dense regions of the Universe (those that correspond to the top 5th percentile in density) at which point the fraction of red dwarfs increases dramatically. Our results offer a roadmap for future studies of dwarf galaxies using LSST commissioning data and subsequently with the survey proper in the next decade.
    • Sarah Brough
      • Title: "Preparing for LSST: first intra-group light analysis in Subaru’s HSC PDR2 data"
      • Abstract: The intra-group light (IGL) forms the predecessor of the intracluster light in clusters of galaxies. The diffuse nature of the IGL makes its study a technical challenge. In this work, we examine the IGL in a group from the Galaxy And Mass Assembly (GAMA) survey using images from the Hyper-Suprime Cam (HSC) Subaru Strategic Program Public Data Release 2 in extraordinary depth. These data were processed with a modified version of the Legacy Survey of Space and Time (LSST) pipeline making this ideal preparation work for upcoming LSST data. We will present our results on the first IGL measurement, distribution, its fraction relative to the group, and color analysis of a group of galaxies at z=0.21 using the most automatic procedure available for this work to date. We use these observations to infer the dominant source in the formation of this important component.
    • Yuan-Yuan Zhang
      • Title: "Characterizing the Evolution of the Intracluster Light with optical images and a tSZ cluster sample"
      • Abstract: Brightest Central Galaxies (BCGs) are characterized by a dense luminous core and an outer halo of diffuse intra-cluster light (ICL). Using a galaxy cluster sample identified by the thermal Sunyaev-Zeldovich effect from the Atacama Cosmology Telescope (ACT), and images from 6 years of Dark Energy Survey Observation, we measure the redshift evolution of the BCG+ICL system over the redshift range 0.2 < z < 0.8. We examine how the stellar content; the parameters of the Stellar Mass – Halo Mass relation (slope, intrinsic scatter, and amplitude); and the ICL’s color and color gradient change with radial extent and lookback time. Our detection of a steeper slope of the SMHM relation when the ICL is included as well as a modest color gradient further supports that the BCG+ICL system grow through a two-phase formation mechanism, likely through the tidal stripping of satellite galaxies.
    • Tony Tyson
      • Title: "LSB completeness requirements for LSST weak lens cosmic shear"
      • Abstract: The LSST 'gold sample' of galaxies will be dominated by r ~ 26-27 mag galaxies at redshifts above 1. LSST probes of dark matter and dark energy will rely heavily on cosmic shear: the correlation of shapes of faint galaxies in the gold sample. Intensity weighted moments of these galaxies need to be complete to ultra-low surface brightness to avoid systematic bias.
    • Ian Dell'Antonio
      • Title: "Joint ICL and shear mapping of nearby clusters with the LoVoCCS survey on DECam"
      • Abstract: The ICL and the dark matter in galaxy clusters both trace the gravitational potential. Because the stars in the ICL are collisionless, any differences between the dark matter and light distributions can also give clues to the nature of the dark matter. The nearest galaxy clusters afford the most detailed view into the distribution of both the ICL and the dark matter. However, they also pose great challenges. I'll talk about the challenges we've encountered using the LSST DM and obs_decam to recover both the shapes of the small faint background galaxies and the ICL on scales of arcminutes and even tens of arcminutes.


    Background Information: the LSB Regime

    This is an important regime, holding much of LSST’s discovery space, and is a key area of current research that will be uniquely expanded upon by LSST’s combination of depth and area. For instance, galaxy evolution is traceable at a granular level through study of intracluster light and tidal streams (both Galactic and extragalactic), while faint dwarf galaxy populations (which are undetectable in past surveys at cosmological distances), via their shallow potential wells, are sensitive tracers of key processes such as tidal perturbation, ram-pressure stripping, and baryonic feedback. The end-stages of high-mass stellar evolution in the Milky Way are also visible through light echoes in supernova remnants, while those of lower mass stars can be seen in the extended diffuse emission of planetary nebulae. The detailed properties of dust grains can be studied via comparative optical and infrared observations of Galactic cirrus at varying elevations above the disk plane, and, on a more local level, comet tails and Zodiacal light contain clues to the history of the Solar System. LSB science therefore spans a broad range of topics accessible by LSST.

    In order to best detect and analyse the low surface brightness light in LSST images there are a number of key preparatory tasks we need to undertake due to the importance of sky foreground subtraction in preserving this light.  To this end, in-kind contributors are working with DM to implement continual tracking of surface brightness preservation metrics into the pipeline, and to revise the pipeline's sky-subtraction algorithm to ensure that all of LSST's potential discovery space is available. With LSST commissioning just around the corner and much effort underway, this is the ideal time to discuss how efforts made towards these preparatory tasks and strategies adopted can solve common problems across different Science Collaborations, to ensure that we are prepared for when data arrives. 

    Aaron E. Watkins, Sarah Brough, Lee Kelvin
    Suggested Audience: 
    Anyone from any astronomical sub-field interested in LSB work, including, broadly, those worried about the pipeline's potential impact on their science
    Data Management
    Applicable to: 
    Tuesday 08/09
    3:30 - 5:00pm
    Tortolita D

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