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  1. Request For Comments
  2. RFC-695

Proposed Update to DIAObject Elements for Host Association

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    • Type: RFC
    • Status: Adopted
    • Resolution: Unresolved
    • Component/s: DM
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      Description

      Draft LSST Change Request (LCR) for the DPDD (LSE-163)

      The following proposed changes are described in the comment below posted on Tue Mar 9 by Melissa Graham, and also in DMTN-151 and in this topic on Community.lsst.org.

      In the DPDD, add these four rows to DIAObject Table (Table 3) along with the three footnotes.

      • potentialHost, unit64[3], "Three extended Objects with lowest separations in Data Release database^FN1^."
      • potentialHostSeparation, float[3], "Separations of potentialHost." 
      • potentialLowzHost, str[1], “External catalog name of the nearest low-z potential host^FN2^.”
      • potentialLowzHostSeparation, float[1], “Separation of potentialLowzHost^FN3^.”

      ^FN1^Separations should be calculated with respect to the transient location using the second moments of each Object's luminosity profile, as described in DMTN-151.

      ^FN2^External catalog will be, e.g., the NGC/IC, unless the community provides one that they deem to be more scientifically useful, as described in DMTN-151.

      ^FN3^Separations will be radial offset in arcseconds unless a community-provided catalog includes galaxy characteristics that would enable an alternative, as described in DMTN-151.

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            mgraham Melissa Graham added a comment -

            Details regarding the updated just posted in the description of this RFC.

            The DM System Science Team proposes to add to the DIAObject table a total of four new elements that will provide more scientifically useful associations for transients and their potential host galaxies. 

            Currently, the two DIAObject table elements that are relevant to the association of transients with their potential host galaxies are: 

            • nearbyObj (unit64[6]) “Closest Objects (3 stars and 3 galaxies) in DR database.”
            • nearbyObjDist (float[6]) “Distances to nearbyObj.” [arcsec]

            Scientifically, this is inadequate for two main reasons:

            1. The radial distance in arcsec matters less than a separation distance which accounts for the galaxies’ spatial luminosity profile (e.g., Sullivan+06).
            2. Transients in the local volume might not be associated with their large extended host galaxies, especially those in the outskirts of their hosts.

            To relieve the first issue, the following two elements should be computed during Alert Production and added to the DIAObject table:

            • potentialHost (unit64[3]) – the objectId for the three Object catalog extended sources with the lowest separation distances
            • potentialHostSeparation (float[3]) – the separation distances for each potentialHost

            The separation distance should be calculated with respect to the transient location using the second moments of each Object's luminosity profile, as described in DMTN-151. All parameters required for the calculation of the separation distances are already planned to be in the DIAObject and Object tables.

            To relieve the second issue, DM will adopt an established catalog of low-redshift galaxies (e.g., from the Revised New General Catalogue and Index Catalogue; TBD) and do a cross match during Alert Production in order to report the name and the radial sky separation of the nearest catalog galaxy:

            • potentialLowzHost (str[1]) – the catalog name of the nearest “low-z” potential host
            • potentialLowzHostSeparation (float[1]) – the distance to potentialLowzHost [arcsec]

            If the community provides a catalog of names and coordinates that they would prefer to be used, it will be adopted. If that catalog includes more information about the galaxy then the value of potentialLowzHostSeparation could be more sophisticated than the radial distance in arcseconds. For example, if distances are included then the offset in kpc could be provided; if sizes are included the number of effective radii could be reported; or if the second moments are included then the separation could be the same as used for potentialHostSeparation.

            Show
            mgraham Melissa Graham added a comment - Details regarding the updated just posted in the description of this RFC. The DM System Science Team proposes to add to the DIAObject table a total of four new elements that will provide more scientifically useful associations for transients and their potential host galaxies.  Currently, the two DIAObject table elements that are relevant to the association of transients with their potential host galaxies are:  nearbyObj (unit64 [6] ) “Closest Objects (3 stars and 3 galaxies) in DR database.” nearbyObjDist (float [6] ) “Distances to nearbyObj.” [arcsec] Scientifically, this is inadequate for two main reasons: The radial distance in arcsec matters less than a separation distance which accounts for the galaxies’ spatial luminosity profile (e.g., Sullivan+06). Transients in the local volume might not be associated with their large extended host galaxies, especially those in the outskirts of their hosts. To relieve the first issue, the following two elements should be computed during Alert Production and added to the DIAObject table: potentialHost (unit64 [3] ) – the objectId for the three Object catalog extended sources with the lowest separation distances potentialHostSeparation (float [3] ) – the separation distances for each potentialHost The separation distance should be calculated with respect to the transient location using the second moments of each Object's luminosity profile, as described in DMTN-151. All parameters required for the calculation of the separation distances are already planned to be in the DIAObject and Object tables. To relieve the second issue, DM will adopt an established catalog of low-redshift galaxies (e.g., from the Revised New General Catalogue and Index Catalogue; TBD) and do a cross match during Alert Production in order to report the name and the radial sky separation of the nearest catalog galaxy: potentialLowzHost (str [1] ) – the catalog name of the nearest “low-z” potential host potentialLowzHostSeparation (float [1] ) – the distance to potentialLowzHost [arcsec] If the community provides a catalog of names and coordinates that they would prefer to be used, it will be adopted. If that catalog includes more information about the galaxy then the value of potentialLowzHostSeparation could be more sophisticated than the radial distance in arcseconds. For example, if distances are included then the offset in kpc could be provided; if sizes are included the number of effective radii could be reported; or if the second moments are included then the separation could be the same as used for potentialHostSeparation.
            Hide
            lguy Leanne Guy added a comment -

            Link to Sullivan et al. 2006 paper mentioned above for interest.

            Show
            lguy Leanne Guy added a comment - Link to Sullivan et al. 2006 paper mentioned above for interest.
            Hide
            jbosch Jim Bosch added a comment -

            :+1: to this from me and Science Pipelines, assuming it hasn't diverged wildly from what was last discussed at SST.

            Show
            jbosch Jim Bosch added a comment - :+1: to this from me and Science Pipelines, assuming it hasn't diverged wildly from what was last discussed at SST.
            Hide
            mgraham Melissa Graham added a comment -

            There was one response from the community about the proposal to update the host association parameters was received, and it is favorable: https://community.lsst.org/t/host-galaxy-association-for-lsst-transients-request-for-comments/4812

            Propose to call this RFC done and submit to the CCB exactly what is in the above description box.

             

            Show
            mgraham Melissa Graham added a comment - There was one response from the community about the proposal to update the host association parameters was received, and it is favorable:  https://community.lsst.org/t/host-galaxy-association-for-lsst-transients-request-for-comments/4812 Propose to call this RFC done and submit to the CCB exactly what is in the above description box.  
            Hide
            mgraham Melissa Graham added a comment -

            Adopting this RFC, implementation proceeds in DM-29731

            Show
            mgraham Melissa Graham added a comment - Adopting this RFC, implementation proceeds in DM-29731

              People

              Assignee:
              mgraham Melissa Graham
              Reporter:
              mgraham Melissa Graham
              Watchers:
              Eric Bellm, Jim Bosch, Kian-Tat Lim, Leanne Guy, Melissa Graham
              Votes:
              0 Vote for this issue
              Watchers:
              5 Start watching this issue

                Dates

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                Updated:
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