Browsing by Subject "integral field spectroscopy"

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Keck-I Mosfire Spectroscopy Of Compact Star-Forming Galaxies At Z Greater Than Or Similar To 2: High Velocity Dispersions In Progenitors Of Compact Quiescent Galaxies
(2014-11) Barro, Guillermo; Trump, Jonathan R.; Koo, David C.; Dekel, Avishai; Kassin, Susan A.; Kocevski, Dale D.; Faber, Sandra M.; van der Wel, Arjen; Guo, Yicheng; Perez-Gonzalez, Pablo G.; Toloba, Elisa; Fang, Jerome J.; Pacifici, Camilla; Simons, Raymond; Campbell, Randy D.; Ceverino, Daniel; Finkelstein, Steven L.; Goodrich, Bob; Kassis, Marc; Koekemoer, Anton M.; Konidaris, Nicholas P.; Livermore, Rachael C.; Lyke, James E.; Mobasher, Bahram; Nayyeri, Hooshang; Peth, Michael; Primack, Joel R.; Rizzi, Luca; Somerville, Rachel S.; Wirth, Gregory D.; Zolotov, Adi; Finkelstein, Steven L.; Livermore, Rachael C.
We present Keck-I MOSFIRE near-infrared spectroscopy for a sample of 13 compact star-forming galaxies (SFGs) at redshift 2 <= z <= 2.5 with star formation rates of SFR similar to 100M(circle dot)yr(-1) and masses of log( M/M-circle dot) similar to 10.8. Their high integrated gas velocity dispersions of sigma(int) = 230(-30)(+40)km s(-1), as measured from emission lines of Ha and [O III], and the resultant M-star-sigma(int) relation and M-star-M-dyn all match well to those of compact quiescent galaxies at z similar to 2, as measured from stellar absorption lines. Since log( M-star/M-dyn)= -0.06 +/- 0.2 dex, these compact SFGs appear to be dynamically relaxed and evolved, i.e., depleted in gas and dark matter (<13(-13)(+17)%), and present larger sint than their non-compact SFG counterparts at the same epoch. Without infusion of external gas, depletion timescales are short, less than similar to 300 Myr. This discovery adds another link to our new dynamical chain of evidence that compact SFGs at z greater than or similar to 2 are already losing gas to become the immediate progenitors of compact quiescent galaxies by z similar to 2.
The Metallicity Dependence Of The Co -> H-2 Conversion Factor In Z >= 1 Star-Forming Galaxies
(2012-02) Genzel, R.; Tacconi, L. J.; Combes, Francoise; Bolatto, A.; Neri, R.; Sternberg, Assaf; Cooper, Michael C.; Bouche, N.; Bournaud, F.; Burkert, A.; Comerford, J.; Cox, P.; Davis, M.; Schreiber, N. M. F.; Garcia-Burillo, S.; Gracia-Carpio, J.; Lutz, D.; Naab, T.; Newman, S.; Saintonge, A.; Shapiro, K.; Shapley, A.; Weiner, B.; Comerford, J.
We use the first systematic samples of CO millimeter emission in z >= 1 "main-sequence" star-forming galaxies to study the metallicity dependence of the conversion factor alpha(CO), from CO line luminosity to molecular gas mass. The molecular gas depletion rate inferred from the ratio of the star formation rate (SFR) to CO luminosity, is similar to 1 Gyr(-1) for near-solar metallicity galaxies with stellar masses above M-S similar to 10(11) M-circle dot. In this regime, the depletion rate does not vary more than a factor of two to three as a function of molecular gas surface density or redshift between z similar to 0 and 2. Below M-S the depletion rate increases rapidly with decreasing metallicity. We argue that this trend is not caused by starburst events, by changes in the physical parameters of the molecular clouds, or by the impact of the fundamental-metallicity-SFR-stellar mass relation. A more probable explanation is that the conversion factor is metallicity dependent and that star formation can occur in "CO-dark" gas. The trend is also expected theoretically from the effect of enhanced photodissociation of CO by ultraviolet radiation at low metallicity. From the available z similar to 0 and z similar to 1-3 samples we constrain the slope of the log(alpha CO)-log (metallicity) relation to range between -1 and -2, fairly insensitive to the assumed slope of the gas-SFR relation. Because of the lower metallicities near the peak of the galaxy formation activity at z similar to 1-2 compared to z similar to 0, we suggest that molecular gas masses estimated from CO luminosities have to be substantially corrected upward for galaxies below M-S.
PHIBSS: Molecular Gas Content And Scaling Relations In Z Similar To 1-3 Massive, Main-Sequence Star-Forming Galaxies
(2013-05) Tacconi, L. J.; Neri, R.; Genzel, R.; Combes, Francoise; Bolatto, A.; Cooper, Michael C.; Wuyts, S.; Bournaud, F.; Burkert, A.; Comerford, J.; Cox, P.; Davis, M.; Schreiber, N. M. F.; Garcia-Burillo, S.; Gracia-Carpio, J.; Lutz, D.; Naab, T.; Newman, S.; Omont, A.; Saintonge, A.; Griffin, K. S.; Shapley, A.; Sternberg, Assaf; Weiner, B.; Comerford, J.
We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2 survey of the molecular gas properties in massive, main-sequence star-forming galaxies (SFGs) near the cosmic star formation peak. PHIBSS provides 52 CO detections in two redshift slices at z similar to 1.2 and 2.2, with log(M-*(M-circle dot)) >= 10.4 and log(SFR(M-circle dot/yr)) >= 1.5. Including a correction for the incomplete coverage of the M-*-SFR plane, and adopting a "Galactic" value for the CO-H-2 conversion factor, we infer average gas fractions of similar to 0.33 at z similar to 1.2 and similar to 0.47 at z similar to 2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the z similar to 1-3 SFGs are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular-gas-star-formation relation for the z = 1-3 SFGs is near-linear, with a similar to 0.7 Gyr gas depletion timescale; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between z similar to 0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M-*, gas fractions correlate strongly with the specific star formation rate (sSFR). The variation of sSFR between z similar to 0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas.
The Virus-P Exploration Of Nearby Galaxies (Venga): The X-Co Gradient In NGC 628
(2013-02) Blanc, Guillermo A.; Schruba, Andreas; Evans, Neal J.; Jogee, Shardha; Bolatto, Alberto; Leroy, Adam. K.; Song, Mimi; van den Bosch, Remco C. E.; Drory, Niv; Fabricius, Maximilian; Fisher, David; Gebhardt, Karl; Heiderman, Amanda; Marinova, Irina; Vogel, Stuart; Weinzirl, Tim; Evans, Neal J.; Jogee, Shardha; Song, Mimi; Gebhardt, Karl; Heiderman, Amanda; Marinova, Irina; Weinzirl, Tim
We measure the radial profile of the (CO)-C-12(1-0) to H-2 conversion factor (X-CO) in NGC 628. The H alpha emission from the VENGA integral field spectroscopy is used to map the star formation rate (SFR) surface density (Sigma(SFR)). We estimate the molecular gas surface density (Sigma(H2)) from Sigma(SFR) by inverting the molecular star formation law (SFL), and compare it to the CO intensity to measure X-CO. We study the impact of systematic uncertainties by changing the slope of the SFL, using different SFR tracers (H alpha versus far-UVplus 24 mu m), and CO maps from different telescopes (single-dish and interferometers). The observed X-CO profile is robust against these systematics, drops by a factor of two from R similar to 7 kpc to the center of the galaxy, and is well fit by a gradient Delta log(X-CO) = 0.06 +/- 0.02 dex kpc(-1). We study how changes in X-CO follow changes in metallicity, gas density, and ionization parameter. Theoretical models show that the gradient in X-CO can be explained by a combination of decreasing metallicity, and decreasing Sigma(H2) with radius. Photoelectric heating from the local UV radiation field appears to contribute to the decrease of X-CO in higher density regions. Our results show that galactic environment plays an important role at setting the physical conditions in star-forming regions, in particular the chemistry of carbon in molecular complexes, and the radiative transfer of CO emission. We caution against adopting a single X-CO value when large changes in gas surface density or metallicity are present.