The Arizona CDFS Environment Survey

 

A preliminary ACES redshift catalog is now available for public use, including >7000 unique sources of which ~5000 have a secure redshift. Below, we provide a link for downloading the current redshift catalog followed by a description of how the catalog is constructed and some initial work on quality assessment. For more information refer to the ACES survey paper [ADS] and/or contact Michael Cooper (m.cooper -at- uci.edu).

The current ACES redshift catalog (as of 2011nov26) includes 13,965 entries, with 14 fields (or tags) per entry. A description of each tag is given in the "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.ACES.2012jun04.fits.gz


Redshift Catalog (ASCII TABLE): zcat.ACES.2012jun04.ascii

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.

Note that our IMACS spectra are relatively low-resolution (R ~ 750). As such, we are unable to resolve the [O II] 3727Å doublet. Thus, the majority of redshift measurements with Q=3 or Q=4 and at z ~ 0.9 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 or Hβ 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 information to discriminate between different potential identifications for a single emission line. For now, the COMBO-17 photometric redshifts, which are included in the redshift catalog, may provide a useful cross-check.

A significant number of sources appear on more than one ACES slitmask. For example, fainter targets were purposefully included on 2 or more masks to increase the net exposure time. Currently, the data from different slitmasks is 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 13,963 entries in the ACES redshift catalog, there are only 7277 unique objects.

From the 7277 unique sources in the ACES catalog, we measure 5022 accurate (Q = -1,3,4) redshifts --- note that this is as of 2011jun01 and that some sources have yet to be inspected and assigned a redshift quality code. As shown in the following plot, there is a tail of sources at z > 1, but the bulk of the objects are at 0.1 < z < 0.8:

Eventually co-adding all data for a given object should improve the ability to identify the redshift for fainter sources. However, treating multiple observations of the same object independently allows us to empirically determine the precision of our redshift measurements. Below is a plot showing the difference in heliocentric-corrected redshift for 596 sources, where data from two distinct slitmasks yielded a high-quality (Q=3,4) redshift for the object. The dispersion of 90 km/s is consistent with what might be expected given the resolution of the IMACS spectra plus some scatter due to variation in slit placement sampling different portion of a galaxy's internal velocity structure.

For more discussion of the survey status, refer to the survey details page.