Abstract
Integral field spectrographs (IFS) have transformed studies of low-redshift spatially resolved galaxies as they provide simultaneous spectral coverage over contiguous spatial regions. Though IFS instruments have been traditionally limited to small fields of view (FOV), on the order of 100 square arcseconds, constraining the extent to which IFS studies can map the most nearby galaxies and conduct galaxy surveys without pre-selected targets. To cost effectively scale up IFS capability in order to observe larger fields, the Visible Integral-field Replicable Unit Spectrograph (VIRUS) utilizes massive replication on an unprecedented 100-fold scale to be able to image ~35,000 fibers over a ~22 arcminute FOV with a single observation. This unprecedentedly large IFS FOV will allow the VIRUS instrument to conduct the Hobby Eberly Telescope Dark Energy Experiment (HETDEX) which will spectroscopically catalog every emission line source in a ~450 square degree area of sky in is 350-550nm bandpass.
With large samples of low-redshift galaxies being traditionally assembled through photometric selection, the HETDEX survey provides an opportunity to build samples of continuum-faint emission line galaxies (ELGs) possibly missed by large photometric surveys. In this talk I will present two studies conducted with these ELG samples. In anticipation of the large sample of low-redshift ELGs that HETDEX will find, we first assembled an unbiased sample of 29 galaxies with [OII] 3727 and/or [OIII] 5007 detections at z < 0.15 from the HETDEX pilot survey (HPS) ELG catalog. We compare the metallicity, stellar mass, and star formation rates (SFRs) for this spectroscopically selected sample to that of the photometrically selected samples of low-redshift galaxies found in the Sloan Digital Sky Survey (SDSS). We find two galaxies that have low metallicity for their mass, falling in a regime that tends to be under sampled in continuum-based surveys as their spectra are typically dominated by emission from newly formed stars. With the first HETDEX data release that surveyed the first ~8 square degrees of the HETDEX field, we specifically search for these low mass and low metallicity galaxies. We assemble a sample of 17 galaxies at z<0.1 with even lower metallicity (7.45 < log(O/H)+12 < 8.12) and stellar masses. We find these galaxies have similar specific star formation rates (sSFRs) as the incredibly rare "blueberry" galaxies found in (Yang+ 2017). These studies both illustrate the power of spectroscopic surveys for finding low mass and metallicity galaxies and reveal that we find a sample of galaxies that are a hybrid between the properties of typical dwarf galaxies and the more extreme blueberry galaxies.
With VIRUS being 156 realizations of the same spectrograph and the first to be replicated on this massive scale, I present analysis that uncovers the statistical variations in performance of these units along with an assessment of cost/tolerance trade offs of scaling up instrument capabilities through massively replicated designs.
Wide field IFS instruments also provide a unique tool for mapping faint surface brightness emission in galaxies to unprecedented extents and sensitivities. Additionally I present a VIRUS-P survey of M82’s northern outflow that I conducted with 27 nights of observing. Despite this classic outflow being studied since its discovery in the 1960s, with VIRUS-P we build the most sensitive and extensive map of the warm ionized gas in the northern outflow to date. I present the first science results from this survey that map the density profile of the outflow out to unprecedented distances from the disk.
Finally, I present the next generation IFS instrument intended to replace VIRUS-P, VIRUS2. The design of VIRUS2 builds on this previous VIRUS replicated concept to scale up its capabilities of a moderately sized FOV (comparable to VIRUS-P) but much higher spatial and spectral coverage. I present the work I did designing the fiber mapping for the novel VIRUS2 fiber feed that allows VIRUS2 to cover both a moderately large field and simultaneous spectral coverage over a wide bandpass. This talk concludes with how the moderately replicated design of VIRUS2 may provide a road map for cost effectively scaling up instrument capabilities for the next generation of extremely large telescopes (ELTs) and how it will open a new window for studying low-redshift galaxies.
