PROPOSAL FOR 30M TELESCOPE Deadline: 12 Mar 2009 Period: 01 Jun Nov TITLE Renaissance in the Green Valley? CO in HI-rich Galaxies

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1 IRAM 300, rue de la Piscine ST. MARTIN d HERES (France) Fax: (33/0) PROPOSAL FOR 30M TELESCOPE Deadline: 12 Mar 2009 Period: 01 Jun Nov 2009 Registration N : Date: For IRAM use TITLE Renaissance in the Green Valley? CO in HI-rich Galaxies Type: Solar system: continuum lines other Extragalactic: continuum CO lines 2 other Galactic: continuum lines circumstel. env. young stel. obj. cloud struct. chem. other ABSTRACT The GASS survey is a large targeted survey at Arecibo designed to measure the HI gas content of 1000 massive galaxies uniformly selected from the SDSS spectroscopic and GALEX imaging surveys. GASS has identified a population of red, early-type galaxies with a significant fraction of atomic gas. We wish to test the hypothesis that this population has accreted gas from the external environment and is currently transitioning from the red to the blue sequence. We propose IRAM 30m CO observations of 15 massive galaxies with HI mass fractions greater than 10%, spanning a range in global NUV-r colour from 2 to 6. We will derive total molecular gas masses and profiles and thereby constrain whether the redder HI-rich galaxies correspond to galaxies caught earlier in the accretion stage, when more of the gas is in a phase and a location where it is unable to form stars. Is this a resubmission of a previous proposal? no 2 yes proposal number(s): Is this a continuation of (a) previous proposal(s)? no 2 yes proposal number(s): Hours requested for this period: 70 LST range(s): from: 09h to: 19h number of intervals: 5 from: 19h to: 05h number of intervals: 2 Special requirements: Large Program pooled obs service obs remote obs polarimeter Scheduling constraints: We.... prefer scheduling in.. the.... first..... half.... of... the.... semester Receivers: EMIR 2 HERA Bolometer Other List of Objects (give most common names) Epoch: J Source RA DEC V LSR GASS :17: :19: GASS :55: :56: GASS :47: :15: GASS :23: :07: GASS :13: :40: GASS :36: :36: GASS :40: :03: GASS :53: :42: GASS :20: :52: GASS :27: :49: GASS :44: :13: GASS :49: :04: GASS :16: :50: GASS :02: :19: GASS :18: :15: Principal Investigator: Guinevere Kauffmann MPA Karl Schwarzschildstr Garching (Germany) Tel: (+49) Fax: (+49) gamk@mpa-garching.mpg.de Other Investigators (name, institution): Barbara Catinella (MPA Germany); Silvia Fabello (MPA Germany); Riccardo Giovanelli (Cornell USA); Javier Gracia-Carpio (MPE Germany); Martha Haynes (Cornell USA); Timothy Heckman (JHU USA); Cheng Li (MPA Germany); Amelie Saintonge (University of Zurich Switzerland); David Schiminovich (Columbia University USA); Linda Tacconi (MPE Germany); ( for additional sources which do not fit here use the \extendedsourcelist macro ) Expected observer(s) Gracia-Carpio,Catinella,Fabello join to this form: scientific aims 2 typed pages ( 4 pages for Large Programs) and 2 pages Figs., Tabs., and Refs.

2 Technical Summary EMIR Note that up to 4 IF signals can be recorded and up to 2 EMIR (always dual polarization) bands can be combined in one EMIR setup. For a summary of EMIR connectivity consult the IRAM Granada home page or the Call for Proposals Transitions = expected line antenna temperature; v = required velocity resolution. T A setup band species transition frequency TA rms v backend a ) GHz mk mk km s 1 1 E0 CO W 2 E1 CO W a ) V: VESPA, W: WILMA, 4: 4 MHz filterbank, 1: 1 MHZ filterbank Observing parameters map size in arcmin; T = requested telescope telescope time per setup setup map size mapping switching T remark No. x y mode a ) mode b ) [h] 1 none WSw 70 Total EMIR time requested: 70 a ) none, OTF (on the fly), R: Raster b ) PSw: position switching, FSw: frequency switching, Wsw: wobbler sw.

3 Renaissance in the Green Valley? CO in HI-rich Galaxies 1 Scientific background: Perhaps the most fundamental new discovery of the large imaging and spectroscopic surveys of galaxies that have been carried out over the past decade is that there are two very distinct populations of galaxies: a red sequence consisting of dense, massive galaxies with little or no ongoing star formation, and a blue cloud consisting of low mass, low surface density galaxies that are still forming stars (e.g. Strateva et al 2001; Kauffmann et al 2003; Baldry et al 2004). The integrated stellar mass density in the red sequence increases by a factor 2 from redshift 1 to zero (e.g. Bell et al 2004, Faber et al 2007), leading to the idea that there is a net migration of galaxies from the blue cloud to the red sequence as a function of cosmic time. In between the red sequence and the blue cloud, the number density of galaxies reaches a local minimum. Because UV/optical colours are sensitive to even a trace amount of unobscured star formation in the galaxy, UV/optical colour-magnitude diagrams have large dynamic range and are extremely effective at picking out a so-called green valley population that lies between the red and the blue clouds (e.g. Schiminovich et al 2007, see Figure 1). The green valley is hypothesized to consist of galaxies that are in the process of transitioning between the red and blue sequences. Because there is net growth in the mass contained in red galaxies from redshift 1 to 0, considerable attention has been given to physical processes that cause star formation to shut down in galaxies, so called quenching mechanisms. Examples include supernova feedback, gas heating by radioloud AGN in clusters, galaxy-wide winds generated from material falling into black holes in accretion disks, ram-pressure stripping of gas, harrassment effects due to galaxy encounters in rich environments, starvation as galaxies run out of fuel etc. Observations of atomic and molecular gas in galaxies play an important role in constraining some of these processes. For example, CO observations of spiral galaxies in the Virgo cluster revealed that although these systems were frequently deficient in HI, they had normal CO luminosities and extents relative to optical properties, lending support to processes such as ram-pressure stripping that selectively remove low density gas in the galaxies (Kenney & Young 1989) Although observations show that there is a net migration of galaxies to the red sequence, we still expect that galaxies might transition through the green valley because they accrete new gas from the external environment (e.g. Kauffmann et al 2007). Microwave background experiments such as WMAP now constrain the fraction of baryonic matter in the Universe to be 4.5% of the critical density (Spergel et al 2007). Remarkably, only 3.5% of all the baryons are currently in stars, the rest must be in the form of gas. One of the major difficulties faced by current galaxy formation models is to explain why the efficiency with which gas cools and condenses onto galaxies is so low. AGN feedback has been proposed as a possible solution, but for galaxies in lower-mass halos, the fraction of radio-loud AGN drops sharply (Best et al 2005). It is thus reasonable to suppose that outside massive clusters, galaxies may still undergo cycles of rebirth through gas accretion. One way to determine observationally if rebirth is occurring, would be to catch objects early in the accretion stage when they have a lot of gas in a phase (HI) and location where it is not yet forming stars. The GASS HI Survey: The GALEX Arecibo SDSS Survey (GASS) is an ongoing large targeted survey at Arecibo, home to the world s largest single-dish radio telescope. GASS is designed to measure the neutral hydrogen content of a representative sample of 1000 galaxies uniformly selected from the SDSS spectroscopic and GALEX imaging surveys, with masses in the range M and redshifts in the range < z < Integration times are set so that we should detect all galaxies with HI mass fractions of 1.5% or more. GASS will produce the first statistically significant sample of massive transition galaxies with homogeneously measured stellar masses, star formation rates and gas properties. Observations started in March 2008, and are expected to be completed over a period of 3 years. More information is available at One of the earliest results to emerge from GASS is that there is indeed a population of red, early-type galaxies with significant amounts of HI gas. These galaxies have global UV/optical colours that place them on the red sequence, early-type morphologies, and SDSS spectra that indicate old stellar populations and no trace of emission lines, but they also have HI mass fractions (evaluated within the 3.5 arcminute Arecibo beam) that reach values in excess of 40%. We have ruled out the presence of any close companions that may confuse our measurements. Interestingly, for some of these systems, the GALEX FUV and NUV images show evidence for extended UV structures. Figure 3 shows SDSS and GALEX images of the 15 targets in this proposal (see below). As can be seen, there are extended UV structures in the 2 reddest 1 These data will form part of the PhD thesis of Silvia Fabello, who has just started a PhD at MPA. She is supervised by Guinevere Kauffmann.

4 galaxies, GASS and 3505, in the form of rings and ripples. Both these galaxies have NUV-r colours that place them firmly in the red sequence, but the HI mass fractions are 0.56 and 0.44! The fact that 15-20% of all elliptical galaxies have significant HI gas content has been known for many years (Knapp, Turner & Cuniffe 1985). However, these galaxies were studied as a separate class of objects, in isolation from the rest of the more normal galaxy population. Our aim is to understand if and how our anomalous HI-rich early-type galaxies relate to the population of normal spirals with similar stellar masses. Proposed observations: We propose IRAM 30m CO observations of 15 galaxies with stellar masses in the range M selected from the GASS parent sample (a larger super-set of galaxies that meet the survey selection criteria). We require that the galaxies already have HI detections from either GASS, the ALFALFA survey (Giovanelli et al 2005), or the Cornell archive (Springob et al 2005), and that the HI mass fraction be greater than 10%. Example Arecibo spectra are shown in Figure 2. In order span the full transition regime, our sample is selected to have a large range in global NUV-r colour from 2 ( edge of the blue sequence) to 6 (oldest galaxies on the red sequence), and to have i < 65 deg, so that the colour estimates are not severely affected by dust attenuation. SDSS and GALEX images of our 15 target galaxies are shown in Figure 3. We have checked that none of these objects have existing CO measurements in the literature. As can be seen, the bluest galaxies in our sample look like ordinary star-forming spirals, but as NUV-r increases, fewer signs of star formation such as HII regions and spiral arms are apparent, and the reddest galaxies look for the most part like normal early-type galaxies, even though they contain as much atomic gas as the bluest objects (right hand panel of Figure 1). The CO observations we propose will allow us to test the hypothesis that the 15 galaxies in our sample constitute an evolutionary sequence, with the reddest objects corresponding to galaxies that have accreted their gas most recently. This proposal is a pilot study to test the above scenario. If successful, we will submit a larger, comprehensive proposal targeting a selection of GASS galaxies for the fall 2009 deadline. Observing strategy: We ask for 5 pointings per galaxy: one at the center, and the others spread around the galaxy. Where the GALEX images show evidence for extended structures, we will ensure that one or more of these outer pointings coincide with the UV detections. We will compute the total molecular gas content of each galaxy and compare it with the HI mass. The extra pointings away from the centers will allow us to derive a rough molecular gas density profile and specify whether the gas is centrally concentrated, as is usually found in spiral galaxies, and whether the degree of central concentration changes systematically as a function of NUV-r colour. The aim is to use the CO observations to constrain the evolutionary state of the gas and to quantify how the anomalous HI-rich early-type galaxies differ when compared to ordinary star-forming spirals with similar stellar masses and atomic gas fractions. If we are truly seeing galaxies that are migrating from the red sequence to the blue cloud, we might hope to uncover mirror images of the HI-deficient spirals studied by Kenney & Young, that is HI-rich early type galaxies that are strongly deficient in molecular gas, or with larger molecular extents compared to optical properties. These straightforward 3mm CO 1-0 observations require average observing conditions; they are ideal for the summer/fall observing period. Assuming molecular masses comparable to the HI masses, and centrally concentrated CO emission, we will need to integrate to an rms of 1-2 mk per point. This is the limit to detect 10 9 M per pointing (for a Galactic X factor), or 10% molecular gas fraction for our lowest mass galaxies. Using the EMIR time estimator (which yields very conservative integration estimates) this is achievable in minutes of telescope time per pointing, including all overheads, depending on weather conditions, and after smoothing to spectral resolutions of km/s. The redshifts of these targets range from z= or cz= ,000 km/s. Thus, all can be observed with one tuning of EMIR, assuming 4 GHz bandwidth per polarization available with the current IF transport and backend capabilities of the 30-m. In case of excellent weather, we will observe simultaneously the CO 2-1 line, but this is not a driver for the proposal. We request a total allocation of 70 hours to complete this pilot study. References Baldry, I. et al 2004, ApJ, 600, 681; Bell, E. et al 2004, ApJ, 608, 752; Best, P. et al 2005, MNRAS, 362, 25; Faber, S. et al 2007, ApJ, 665, 265; Giovanelli, R. et al 2005, AJ, 130, 2598; Kauffmann, G, et al 2003, MNRAS, 341, 54; Kauffmann, G. et al 2007, ApJS, 73, 173, 357; Kenney, J. & Young, J. 1989, ApJ, 344, 171; Knapp, G., Turner, E. & Cuniffe, P.E. 1985,AJ, 90, 454; Morganti, R. et al 2006, MNRAS, 371, 157; Schiminovich, D. et al 2007, ApJS, 173, 315; Springob, C. et al 2005, ApJS, 160, 149; Spergel, D. et al. 2007, ApJS, 170, 377; Strateva, I. et al 2001, AJ, 122, 1861.

5 Figure 1: Left: UV/optical colour-magnitude diagram showing the blue cloud, red sequence and green valley. Right: The location of our 15 proposed targets are shown as black points in the plane of atomic gas fraction versus NUV-r. The location of blue sequence spirals is shown by the blue points (from ALFALFA). The location of typical red and dead ellipticals is shown as the red ellipse (Morganti et al. 2006). Figure 2: HI spectra from Arecibo for two of the galaxies in our sample. GASS No. RA DEC z iso rad inclin NUV-r log M* M HI /M* Table of the target galaxies: iso rad is the SDSS isophotal r-band diameter of the galaxy in arcseconds, inclin is the inclination in degrees.

6 Figure 3: SDSS g,r,i colour images (top) and GALEX FUV/NUV(bottom) images of our 15 target galaxies. The galaxies are arranged in order of increasing NUV-r colour. Images are 2 2 arcminutes for both the optical and UV images (but note that GALEX has a resolution of 5 arcsec). There are extended UV structures in the 2 reddest galaxies, GASS and Extended UV structures are also visible in 23685, 1977, 9948.