Spectroscopy in Cosmology and Galaxy Evolution 2005-2015 Conference Summary

1. Spectroscopy in Cosmology and Galaxy Evolution2005-2015Conference Summary Michael Strauss Princeton University

2. There are many imaging surveys planned in the optical (e.g., Pan-STARRS, VISTA, LSST), and near-IR (UKIDSS, DUNE) • People here don’t need convincing that real spectroscopy is at least as valuable. • It is through spectra that we determine the astrophysics of individual objects. • But photo-z’s remain powerful, as argued by Wolf, Hildenbrandt, and Benítez. • The combination of imaging and spectroscopy is particularly valuable (indeed, crucial, says Gunn). One can use cross-correlation of the two to constrain redshift distributions (Newman).

3. Spectra “good enough for a redshift”? • Focussed surveys to get redshifts only can go much quicker than more comprehensive projects (PRIMUS, ADEPT, HETDEX, FASTSOUND). This is a fine approach to baryon oscillation projects. • But high S/N spectra are tremendously valuable for stellar populations, M/L, ages, star formation rate, metallicities, velocity dispersions, emission-line diagnostics, AGN activity (Thomas, me), serendipity…

4. Serendipity… Gravitationally lensed galaxies behind LRGs; Bolton Ly emitters in DEEP2; Davis

5. We’re never satisfied with the quality of spectra we have… • Excellent spectrophotometry was emphasized by Panter and others. • Broad wavelength coverage, including NIR and into Spitzer bands (Maraston, Gunn). The advent of FMOS and SIDE are particularly exciting here. • High S/N, even for faint objects, as emphasized by Smith, Chilingarian, and others. • High resolution (R=5000), to study dwarfs, and to resolve the OH forest. • Studies of environment effects on galaxy properties, especially clusters (Wolf, Maurogordato, Khochfar, Tanaka, Kovac).

6. We also need spatially resolved spectroscopy of galaxies! • The aperture effects in SDSS are severe, making it difficult to compare spectra at low and high redshifts. • There is much to be learned from internal kinematics of galaxies, as, e.g., the SAURON survey has shown us for nearby ellipticals. Multiple deployable IFU’s? (KMOS, also SIDE with micro-IFU’s).

7. At what redshift do we want to work? • Shanks argues that the z<1 universe of galaxies is “solved”. But we saw lots of reasons to study it in more detail, including “archeology” via detailed spectral modelling of z~0 galaxies (Brinchmann, Maraston, Panter, Kauffmann, Gonzàlez-Delgado and others). • We are still trying to understand observationally the merger rate, and the drop in star formation rate since z~1 (Tresse). • We shouldn’t forget the archeology of studying our own Milky Way in detail, to learn about the formation of the galaxy we know best (SEGUE, RAVE, and other surveys).

8. The high redshift universe is interesting too! • Galaxy populations change dramatically at z>1.5. We argue over the galaxy census at z=3 and its connection to low redshift. • It is difficult work. Even getting redshifts at z>1.4 requires wide wavelength coverage, including NIR. Physical studies are even more difficult, but are very important. It will be a long time before we can hope for SDSS-like spectra at high z. • VVDS (Le Fèvre) and DEEP2 (Davis) show we can do large surveys at z~1, but we’re still very cosmic-variance limited. • We heard almost nothing about surveys at z≥3.

9. There is much work to be done on understanding UV spectra of galaxies (and stars!; Brinchmann, Heap), needed for high-z surveys. Emission-line ratios are interestingly different at z=2-3 and z=0!

10. We also haven’t mentioned other types of spectroscopy: • SKA: A neutral hydrogen spectroscopic census out to z~1: the cold gas component of galaxies. • The IGM, as studied through the Ly forest of quasars (or galaxies for the ELTs), or via UV emission detected by dedicated telescopes (Tresse, White).

11. BAO or galaxy studies? • Why is there a choice? Surveys like SDSS have shown that you can do cosmology and get spectra to study galaxy properties at the same time. This of course gets increasingly difficult as you get fainter… • BAO is a growth industry (Nichol, Schlegel, Totani, Shanks). We can argue about whether it is “fundamental” and where we should put all our energy, but the acceleration of the universe is an astronomically observed fact, and we need to probe it in as many ways as we can.

12. Making surveys work: it is not just building an instrument! • Line up funding in advance! (SDSS’ mistake…) • Get strong project management (another SDSS mistake). • Build your system with specific surveys in mind! • Be patient. • Software is at least as important as the hardware. Don’t cut corners. Automate redshift estimation! • Those that build the hardware and the survey will be too tired/busy to do the science; make sure young people have plenty of opportunity and freedom to lead the science analyses. And make sure that the community recognizes who did the work! (Nichol, White) • Outreach (Letterman, Google Earth…)

13. Wide-field spectroscopy in the future • We heard about many wonderful projects that will soon get underway or are poposed: Wigglez, FMOS , , zCOSMOS, WMOS, KMOS, SIDE, BOSS, HETDEX (Sorry to Tom for the acronyms!) • There are other related projects not discussed here: LAMOST, ADEPT, SPM, RAVE, SKA, SPACE. No doubt I’m missing some important ones… • The field will remain vibrant with the advent of the 20-40 meter telescopes (Colless). Moreover, there will be plenty of survey work to keep the 4- and 8-meters busy for at least several decades.

14. Let us close by thanking Paco, Antonio and Christian for organizing such a scientifically productive meeting in such a beautiful and fascinating place!