Multi-Object Reverberation Mapping


Photo of Niel Brandt
Niel Brandt
Pennsylvania State University


A multi-epoch spectroscopic survey designed to enable use of the reverberation mapping technique to study the structure of broad-line regions in AGN and quasars

Finding Targets

An object whose ANCILLARY_TARGET2 value includes one or more of the bitmasks in the following table was targeted for spectroscopy as part of this ancillary target program. See SDSS bitmasks to learn how to use these values to identify objects in this ancillary target program.

Program (bit name) Bit number Target Description Number of Fibers
RM_TILE1 54 AGN selected for reverberation mapping study at high priority 230
RM_TILE2 55 AGN selected for reverberation mapping study at lower priority 619


The broad emission lines in AGN spectra can have flux variations correlated with variation in the continuum, but with a time delay interpreted as the mean light-travel time across the broad-line region. Measuring this time delay — a technique known as reverberation mapping — allows researchers to study the structure and kinematics of the broad-line regions of AGN.

This program obtained repeated spectroscopy of 849 spectroscopically-confirmed quasars over 30 epochs, with the goal of studying the variability of this sample. Observations were scheduled with a cadence of four to five ays, weather permitting, with a goal of five epochs per month between January and June 2014. Typical exposure times were 2 hours; thus, the final data from this program comprise a 60-hour effective exposure time for targets in this field.

The survey is described in Shen et al. (2015).

The high cadence sequence of observations and the resulting deep co-added spectra allow additional unique analyses beyond reverberation mapping. For example, the sample has been used to measure host stellar velocity dispersion for 88 broad-line quasars at 0.1 < z < 1 (Shen et al. 2015), which can be used to spectroscopically characterize general quasar variability, and to identify variability of intrinsic quasar absorption lines.

Target Selection

Previous spectroscopy of the PS1 Medium Deep Field MD07 (α = 213.704, δ = +53.083) provided redshifts of roughly 1,200 quasars in the redshift range 0 < z < 5 over the area of a single plate. The sample was limited to quasars with i < 21.7.

Lower-redshift quasars (whose time delay should be easier to measure) were given higher priority, and these are indicated by the RM_TILE1 target class; essentially all of these targets were assigned a fiber.

Higher-redshift targets, indicated by the RM_TILE2 target class, were tiled with the remaining fibers.

Three plates containing identical science targets were drilled at varying hour angle to ensure that the field was visible for six months. Each plate was given the normal number of sky fibers (80), but was allocated a substantially larger number of standard star fibers (70 rather than the usual 20) to allow more rigorous tests of spectrophotometric calibration.


Shen, Y., et al. 2015, ApJS, 216, 4