Magellan/IMACS Spectroscopy of the UDS and COSMOS Fields

 

The current version of the UDS/COSMOS redshift catalogs contain 475/301 unique sources of which 352/266 have a secure redshift, respectively. Below, we provide (password-protected) links for downloading the current proprietary redshift catalogs followed by a description of how the catalogs are constructed and some initial work on quality assessment. For access to the redshift catalogs, contact Michael Cooper (m.cooper -at- uci.edu).

UDS Redshift Catalog:


The current UDS redshift catalog (as of 2011jan10) includes 502 entries, with 12 fields (or tags) per entry. A description of each tag is given in the UDS “ztags” primer. We package the catalog as a BINARY TABLE in a standard FITS file, but also provide a version formatted as a space-deliminated ASCII table.

Redshift Catalog (FITS BINTABLE): zcat.UDS.2011-01-10.fits.gz


Redshift Catalog (ASCII TABLE): zcat.UDS.2011-01-10.dat

The redshift measurement for each object in the ACES database is inspected by eye and assigned a quality code (Q = -2, -1, 0, 1, 2, 3, 4) based on the determined accuracy of the redshift value. The break-down of the quality codes is like so

Quality Code

Q = -2

Q = -1

Q = 0

Q = 1


Q = 2


Q = 3

Q = 4

Brief Description

Object was effectively unobserved

Object is identified as a star (i.e., z ~ 0)

Object has yet to be inspected; quality still to be assigned.

Redshift unlikely to be recovered for this source; redshift value in catalog is not meaningful.

Redshift may yet to be recovered for this source; redshift value in catalog is not meaningful.

Secure redshift

Very secure redshift.

In the UDS redshift catalog, 352 sources have an accurate redshift, with a quality code of Q = -1, 3, or 4. The median redshift for this sample of 352 sources is z ~ 0.65, with the redshift distribution shown in the following plot:

Note that our IMACS spectra are relatively low-resolution (R ~ 1200). As such, we are unable to resolve the [O II] 3727Å doublet in many cases. Thus, a few of the redshift measurements with Q=3 at z ~ 1 or higher are based on the identification of a single emission line (as [O II]). Now, when a single emission line is visible at λ > 7500Å, the identification is increasingly likely to be [O II], as Hα, Hβ, or [O III] emission at such wavelengths would often lead to another bright emission line falling into the spectral window. We are working on the use of broad-band color/photo-z information to discriminate between different potential identifications for a single emission line.

A small number of sources appear on more than one slitmask. Currently, the data from different slitmasks are being analyzed independently (i.e., not being co-added). As such, a target that appears on 2 separate slitmasks will appear twice in the redshift catalog. Thus, while there are 502 entries in the redshift catalog, there are only 475 unique objects (as of 2011jan10).

COSMOS Redshift Catalog:


The current COSMOS redshift catalog (as of 2011jan10) includes 301 entries, with 12 fields (or tags) per entry. A description of each tag is given in the COSMOS “ztags” primer. We package the catalog as a BINARY TABLE in a standard FITS file, but also provide a version formatted as a space-deliminated ASCII table.

Redshift Catalog (FITS BINTABLE): zcat.COSMOS.2011-01-10.fits.gz


Redshift Catalog (ASCII TABLE): zcat.COSMOS.2011-01-10.dat

The redshift measurement for each object in the database is inspected by eye and assigned a quality code (Q = -2, -1, 0, 1, 2, 3, 4) based on the determined accuracy of the redshift value. The break-down of the quality codes is the same as given above. In the COSMOS redshift catalog, 266 sources have an accurate redshift, with a quality code of Q = -1, 3, or 4. The redshift distribution for these 266 sources is shown below.