REFUELING TRANSITIONS and the RISE and FALL of BULGED SPIRAL GALAXIES Sheila J

draft Preprint typeset using LATEX style emulateapj v. 5/2/11 THE GAS-RICHNESS THRESHOLD MASS IS NOT THE BIMODALITY MASS: REFUELING TRANSITIONS AND THE RISE AND FALL OF BULGED SPIRAL GALAXIES Sheila J. Kannappan1, David V. Stark1, Kathleen D. Eckert1, Amanda J. Moffett1, Lisa H. Wei2,3, D. J. Pisano4,5, Andrew J. Baker6, Stuart N. Vogel7, Daniel G. Fabricant2, Seppo Laine8, Shardha Jogee9, Mark A. Norris1, Loren E. Hough10, Natasha Lepore11, Jennifer Weinberg-Wolf1 draft ABSTRACT Drawing on three statistically robust z = 0 data sets, we show that two galaxy mass scales <1 dex apart | the \gas-richness threshold mass" and the \bimodality mass" | mark the demographic rise and fall of bulged Sa{Sc spirals. Below the threshold scale, gas-dominated, mainly bulgeless Sd{Im galaxies are more common, while above the bimodality scale, gas-starved E/S0s are the norm. Notwithstanding these results, we show that the correlation of gas-to-stellar mass ratio Mgas=M∗ with non-covariant total mass estimators is poor compared to the correlation of Mgas=M∗ with long-term specific star formation rate <SSFR>LT, averaged over the hundreds of Myr timescales probed by ground-based ultraviolet/blue minus near-infrared colors. This tight correlation of past-averaged star formation with current gas richness suggests that most galaxies are routinely refueled. We argue that the threshold and bimodality scales are indirect reflections of transitions between three refueling regimes within the Mgas=M∗ vs. <SSFR>LT correlation: \accretion dominated," \processing dominated," and \quenched." Bulgeless late types are accretion dominated, enjoying largely continuous refueling and stellar mass growth of order 100% per Gyr regardless of any inefficiency in gas processing. Mild quenching yields bulged Sa{Sc galaxies that are processing dominated, efficiently consuming freshly accreted gas and subject to bursty fluctuations in gas richness and star formation, with the largest bursts creating blue compact states. Total quenching yields red and dead E/S0s with <5% stellar mass growth per Gyr. We employ a Monte Carlo simulation to demonstrate that possibly abrupt transitions between the three regimes would be consistent with the apparently smooth dependence of Mgas=M∗ on M∗ across the threshold and bimodality scales, due to covariance combined with known observational biases and uncertainties. Apart from this analysis, we also provide a useful compilation of photometric, kinematic, and HI data for the Nearby Field Galaxy Survey, including revised HI fluxes and linewidths. Subject headings: galaxies: evolution 1. INTRODUCTION abundance of disk-dominated vs. bulge-dominated galax- Galaxies grow both by merging and by fresh gas ac- ies across a broad range of environments in the universe cretion. Hierarchical models that follow the merger his- (e.g., Navarro & White 1994; Abadi et al. 2003; D'Onghia tories of galaxies and their host dark matter halos suc- & Burkert 2004; Martig et al. 2012). Broadly speaking, cessfully explain the large-scale structure of the universe, this failure reflects the disk-destroying nature of stellar- yet these models have difficulty reproducing the relative mass dominated mergers (and is therefore mitigated to the extent that models produce \quiet" merger histories, 1 Department of Physics and Astronomy, University of North such as those typical for field galaxies; Weinzirl et al. Carolina, 290 Phillips Hall CB 3255, Chapel Hill, NC 27599, 2009; Fontanot et al. 2011), as well as the extreme loss of USA; [email protected] gas angular momentum in some simulations (which may 2 Harvard-Smithsonian Center for Astrophysics, 60 Garden St. MS-20, Cambridge, MA 02138, USA be mitigated by implementing star formation feedback 3 Atmospheric and Environmental Research, 131 Hartwell Av- and/or higher mass and force resolution, e.g., Weil et al. enue, Lexington, MA 02421, USA 1998; Governato et al. 2007). On the other hand, gas-rich 4 Department of Physics, West Virginia University, P.O. Box mergers are much less destructive and may even help to 6315, Morgantown, WV 26506, USA 5 Adjunct Assistant Astronomer, National Radio Astronomy build disks; such mergers are expected to predominate at Observatory, P.O. Box 2, Green Bank, WV 24944, USA low galaxy masses and/or early epochs (e.g., Robertson 6 Department of Physics and Astronomy, Rutgers, the State et al. 2006; Hopkins et al. 2009; Stewart et al. 2009). In University of New Jersey, 136 Frelinghuysen Road, Piscataway, addition, recent theoretical advances suggest that \cold- NJ 08854-8019, USA 7 Department of Astronomy, University of Maryland, College mode" gas accretion, which delivers fresh gas to galax- Park, MD 20742-2421, USA ies via bulk flows that never reach the halo virial tem- 8 Spitzer Science Center, Caltech, MS 220-6, Pasadena, CA perature, may account for a larger percentage of galaxy 91125, USA 9 Department of Astronomy, University of Texas at Austin, growth than merging does, still within the hierarchical Austin, TX 78712, USA merging paradigm (Kereˇset al. 2005). Cold flows can in 10 Department of Physics, University of Colorado at Boulder, principle provide angular momentum and enable rapid Boulder, CO 80309-0390, USA growth of large-scale disks (Stewart et al. 2011; but see 11 Department of Radiology, University of Southern Califor- nia and Children's Hospital Los Angeles, 4650 W Sunset Blvd, also Sales et al. 2012 regarding spheroid formation in the MS#81, Los Angeles, CA 90027, USA presence of multiple misaligned flows). These flows are 2 Kannappan et al. predicted to dominate in halos below a critical \shock- V ∼ 30 km s−1 (Mac Low & Ferrara 1999). Blowaway heating stability" mass (Birnboim & Dekel 2003) and in near V ∼ 100 km s−1 would be in any case hard to rec- large-scale cosmic filaments and walls (Kereˇset al. 2005), oncile with the fact that \high-mass dwarf" galaxies are where observational signs of such flows have indeed been typically gas rich rather than gas poor (e.g., Bettoni observed (Zitrin & Brosch 2008; Stanonik et al. 2009; et al. 2003; Kannappan 2004). Still, the physics of the Narayanan et al. 2010; more generally, see also Giavalisco ISM does change at the threshold scale. Garnett (2002) et al. 2011; Ribaudo et al. 2011; Churchill et al. 2012; reports that effective yields (derived from metallicities Rauch et al. 2012). and gas fractions) start dropping for V . 125 km s−1, Clearly gas physics lies at the heart of understand- which he interprets to reflect increasing metal loss due ing the disky morphologies and overall growth history to supernova-driven winds in a closed box model. In a of galaxies, and the mass dependence of this intercon- non-closed box model, this result may be interpreted as nection is of key interest. Two galaxy mass scales have reflecting a shift toward higher gas richness, seen on both been previously noted as important transition points in the red and blue sequences by Kannappan (2004), with morphology, gas richness (defined as gas-to-stellar mass gas-dominated galaxies becoming typical of the blue se- ratio in this paper), and star formation history: the quence below the threshold scale (where we assume a cor- \bimodality scale," typically identified with stellar mass rection to the M∗ scale used by Kannappan 2004 follow- 10 M∗ ∼ 3 × 10 M⊙ (Kauffmann et al. 2003a), which cor- ing Kannappan & Wei 2008; see also x 3.1 herein). Calcu- − responds to rotation velocity V ∼ 200 km s 1 (see x 3 lations by Dalcanton (2007) suggest that this gas richness herein) and a second transition scale typically identi- transition is essential to explain the effective yield trend fied with V ∼ 100{125 km s−1 (Dekel & Silk 1986; Gar- seen by Garnett (2002), along with low star formation nett 2002; Dalcanton et al. 2004), which corresponds efficiency (in the sense of star formation rate divided by 9:5−10 to a range of stellar masses M∗ ∼ 10 M⊙ (see gas mass; we will revisit the concept of efficiency in the x 3 herein). We refer to the latter as the \gas-richness presence of accretion in x 4.4.1). threshold scale" following Kannappan et al. (2009, here- In an influential study of edge-on, \bulgeless" disk after KGB). galaxies, Dalcanton et al. (2004) reported another, pre- The bimodality scale marks the crossover point in rela- sumably related change in ISM physics at the thresh- tive abundance of young disk-dominated vs. old spheroid- old scale: thin, concentrated dust lanes emerge abruptly − dominated stellar populations (Kauffmann et al. 2003a). above V ∼ 120 km s 1. Moreover, despite the authors' As traced by late-type vs. early-type morphology, this best efforts to select for bulgeless morphology, in prac- transition appears to shift downward in mass over cos- tice their high-quality follow-up imaging reveals a small mic time (Bundy et al. 2005). Equivalently, the bimodal- \three-dimensional" bulge in every sample galaxy above − ity scale marks a shift in the relative number density of V ∼ 120 km s 1, suggesting a link between changes in galaxies on the red and blue sequences in u − r color vs. gas physics and galaxy structure. The onset of inevitable stellar mass M∗ parameter space (Baldry et al. 2004), bulges (also seen by Bell 2008) occurs simultaneously which are associated with \red and dead" galaxies that with a sharp decline in the population of \blue-sequence have a strong 4000A˚ break (indicating little star forma- E/S0s," i.e., morphologically defined E/S0s found on the tion in the last Gyr) and blue star-forming systems, re- blue sequence in u − r vs. M∗, above the threshold scale. spectively. The red sequence appears to be “filling in" These predominantly non-cluster galaxies are identified from the top down over cosmic time, although both se- by KGB as gas-rich merger remnants rebuilding disks (al- quences extend over a wide range in mass, and differ- though higher-mass blue E/S0s are more often in the pro- ent quenching processes | e.g., merger-driven gas de- cess of quenching, especially above the bimodality scale; pletion, feedback from starbursts or active galactic nuclei Schawinski et al.

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