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									                           Overlap Between Optical/Near-IR Selected Z~2 Galaxies and Mid-IR
                                                                                           Naveen Reddy, Chuck Steidel (Caltech)
                                                                              We have examined X-ray and mid-IR data for samples of optical and near-IR selected galaxies
                                                                              based on their UGR, BzK, and J-K colors. We find a 70-80% overlap between samples of optical
                                                                              and near-IR selected star forming galaxies. Stacked X-ray data indicate galaxies in these samples
                                                                              have similar SFR distributions; galaxies with the reddest near-IR colors appear to be passively
                                                                              evolving. The only significant difference between optical and near-IR selected massive galaxies
                                                                              may be the presence of star formation in the former. Spitzer/MIPS data indicate galaxies in optical
                                                                              and near-IR samples span a large range in infrared luminosity, from LIRGs to ULIRGs. LIRG-type
                                                                              galaxies appear to follow the local dust obscuration law, whereas the UV luminosity and spectral
                                                                              slope underestimate the infrared luminosities of >10^12 L galaxies.

                          Sample Selection                                                                             Stellar Populations
→ GOODS-North Data: Subaru/ACS optical; Chandra X-ray; Spizter IR/MIR;
                                                                                                                                                                                                     Dust Absorption in Z~2 Galaxies
Keck Spectroscopy; Palomar JK imaging; select z~2 candidates according
to their colors
                                                                                                                                                                              → most optical/near-IR selected galaxies
                                                                                                                                                                              follow the Meurer relation, except the
                                                                                                                                                                              most luminous ones and the youngest
                                                                                                                                                                              ones with ages <100 Myr; latter may be
                                                                                                                                                                              tied to PAH formation timescale
                                                                                                                                                                              → stars have blue R-K colors as well as
                                                                                                                                                                              some low-z galaxies
                                                                                                                                                                              → use magnitude cut of R~23 mag to
                                                                                                                                                                              reject interlopers (will also exclude some
                                                                                                                                                                              bright z~2 galaxies)

                                                                                                Reddest galaxies with (z-K)>3 must have declining star formation histories
       → General overlap between optical (UGR) and near-IR
       (BzK;DRG) samples, but photometric errors are important!                                                  Selecting Massive Galaxies

                            Stacking Results                                                                                                                                  →luminous galaxies (>10^12 L)
                                                                                                                                                                              generally lie above Meurer relation: the
         Stacked X-ray emission for X-ray undetected galaxies:                                                                          Only significant difference           UV luminosity and slope underpredict the
                                                                                                                                       between optical and near-              bolometric luminosities of these
          SFR distributions are similar between the samples, but are a                                                                IR selected galaxies may               ultraluminous galaxies
         strong function of K-band magnitude.                                                                                          be the presence of some
                                                                                                                                       unobscured star formation

                                                                    Turnover in SFR!

                                                                                                  Mid-Infrared Properties Optical/Near-IR Galaxies
                                                                                                                                                                                →70-80% overlap between optical/near-IR selected samples of z~2 galaxies after
                                                                                                                                                                                removing contaminants; photometric scatter accounts for most of the near-IR selected
                                                                                                                                                                                galaxies missed by the optical criteria, and vice versa

              Near-IR galaxies not selected optically have SFRs
             similar to those that are optically-selected                                                                                                                       →Stacking X-ray emission shows samples have similar SFR distributions; galaxies
                                                                                                                                                                                with the reddest near-IR colors are passively evolving

                                                                                                                                                                                → Spitzer/IRAC data (combined with X-ray results) suggest SFR may be only
                                                                                                                                                                                difference between massive galaxies selected in the optical and near-IR

                                               Larger SFRs for galaxies                                                                                                        → Spitzer/MIPS data indicate optical and near-IR selected galaxies span a wide
                                              with red z-K colors                                                                                                               range in infrared luminosity; most galaxies at z~2 are have luminosities comparable to
                                                                                                                                                                                LIRGs and appear to follow the Meurer dust-obscuration relation for local starbursts;
                                                                                                                                                                                ultraluminous galaxies in all samples have higher infrared luminosities than predicted
                                                                                                                                                                                by the Meurer relation based on the UV luminosity and/or UV spectral slope.
                                                                                                Optical/Near-IR Selected Galaxies span large range in infrared luminosity

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