Secular evolution in the green valley. Thiago S. Gonçalves Karín Menéndez-Delmestre João Paulo Nogueira-Cavalcante Kartik Sheth Chris Martin

Transcription

1 Secular evolution in the green valley Thiago S. Gonçalves Karín Menéndez-Delmestre João Paulo Nogueira-Cavalcante Kartik Sheth Chris Martin

2 Bimodality in colors z~0.1 Wyder+07 z~1.0 Willmer+06

3 The mass flux density Stellar mass Number density Transition timescales

4 Spectroscopic indices to determine star formation history of galaxies Kauffmann+03

5 NUV - r Fast evolution Green valley Slow evolution t (Gyr) z ~ 0.1 γ=20 Gyr -1 no such trend is apparent in the data there is no redshift dependence at all in the index values. Martin Time Variations and Delays t < t0 In comparing the transitional, red, and blue sequence mass fluxes, we have glossed over time delays in the transition from blue to the red sequence. These could impact the present measurement if there are variations in the mass t > flux rate t0over the cosmic timescales spanned by the DEEP2 and COMBO-17 observations. We have determined typical quench rates to be 1Y1.5 Gyr 1. With this rate, evolution from blue to our transitional color takes 3 Gyr,withasimilaradditionalintervaltoreachtheredsequence. Strictly speaking, we must compare the mass flux rate now with the blue sequence evolution 3 Gyr in the past and the red sequence evolution 3 Gyr in the future. The results of Faber et al. (2007) suggest that the mass flux rate is roughly constant, although the rate may be higher in the highest redshift bin. It will be of some interest to measure the transitional flux at higher redshifts to determine whether it is evolving with time. The mass flux density in the green valley and the evolution of the red sequence agree γ=0.5 Gyr -1

6 The universe was forming stars more at a faster rate in the past Hopkins+06

7 Downsizing!! Noeske+07

8 The CM diagram and the Luminosity function at z~ Φ (Mpc -3 Mag -2 ) z ~ 0.8 z ~ 0.1 NUV - r 4 2 Φ(Mpc -3 Mag -1 ) M r M r Luminosity functions are systematically shifted towards brighter magnitudes at higher redshift Gonçalves+12

9 D n (4000) vs H d,a H δ,a (A) Coadded spectra W/O correction W/ correction NUV r = 4.0 (models) Dn(4000) Gonçalves <r> = <r> = <r> = <r> = <r> = λ Deepest spectra ever taken of green valley galaxies (8-9hr Keck)

10 Galaxies move across the green valley more rapidly at z~0.8 Fraction More rapidly z~0.8 z~ γ (Gyr -1 ) Gonçalves+12

11 log ρ (M sun yr -1 Mpc -3 ) W/O correction W/ correction z Mass flux density happens in fainter, less massive galaxies in recent times The mass flux density evolution agrees with the growth of the red sequence (Faber et al. 2007) log ρ (M sun yr -1 Mpc -3 ) Brighter, more massive M r z ~ 0.8 z ~ 0.1

12 Top-down scenario for the evolution of the red sequence: Massive red galaxies form earlier from quenching of star formation in massive spirals This process moves to low-mass galaxies in the local universe Downsizing! Borch+06

13 Evolution of the CM diagram Slow Fast!13

14 Physical processes? Figure 6. Red fraction in SDSS as functions of stellar mass and environment. Peng+10!14

15 Bars and secular evolution EGS, HST/ACS, z~0.8 Lotz+08 GV galaxies By-eye classification: 10-15% Compared to ~30% total (Sheth+08) Galaxy Zoo + HST? (Talk by E. Cheung) Nogueira-Cavalcante+, in prep Ellipticity determination (Menéndez-Delmestre+07)!15

16 ! Preliminary!16

17 Slow Fast!17

18 Summary Through deep spectroscopy, we can estimate the star formation history of galaxies at z~0.8 The evolution of the mass flux density: at earlier times, faster transtion happening in more massive galaxies Top-down scenario: more massive galaxies in the red sequence were formed earlier, and less massive objects fill in at later times Bars appear to indicate slow quenching. More secular evolution at low-z?

19 Correcting for extinction Contamination: Up to 70% of the green valley galaxies are dusty starbursts detected in MIPS 24um Extinction-corrected CM diagram NUV - r 4 2 GV NUV - r Gonçalves+12 M r M r

20 Star formation acceleration (SFA) GALAXY PHYSICAL PARAMETERS (GPP) ACROSS THE UVOCMD. Martin, Gonçalves et al. 2013!20

21 Example spectra Spectral features are distinguishable down to r~24 r ~ 21.5 r ~ 22.5 r ~ 23.5 Gonçalves+12

22 Bars come AFTER quenching? Increased bar fraction in the red sequence Masters+12!22

23 8 FANG ET AL < log M < < log M < < log M < NUV r 3 2 σgv = < log M < σgv = < log M < σgv = < log M < No evolution in central density or velocity dispersion after quenching σgv = σgv = 0.18 σgv = 0.18 SF QUENCHING AND INNER STELLAR MASS DENSITY ! 15 We will be able to correlate quenching timescales with bar properties - at low AND that the outer parts of all galaxies in a mass bin have similar values of (R), especially at higher mass. This stands in high redshift contrast to the SB profiles, where we noted that blue galax- log 1 [M kpc ] Figure 6. NUV-r vs. 1, plotted for the volume-limited sample in six stellar mass bins. Values of 1 are computed from the mass density profiles discussed in Section 2.3. The7error bars<indicate median error in 1 for blue,<green, red galaxies in each mass Dotted lines indicate the division between 9.75 log M <the log Mand < bin. < log M <gray blue, green, and red galaxies. The hook -shaped distribution in seen in nearly every mass bin. The horizontal scatter in dex of the distribution in the green valley is indicated at the 6 bottom of each panel. Assuming that galaxies evolve at fixed mass, this suggests that galaxies in the blue sequence build up their bulges (i.e., increase 1 ) and then quench and redden. The near-vertical distribution of green and red galaxies suggests that inner bulge buildup does not continue (much) once a galaxy leaves the blue sequence. In addition, the distribution marches toward higher 1 with increasing stellar mass. Dotted red lines indicate the value 5 80% of the red galaxies lie in each mass bin. of 1 above which NUV r M/L relation4in Figure 3. Despite their brighter outer disks, blue galaxies have nearly identical outer mass profiles as red galaxies. This3 can be explained as a consequence of the lower mass-to-light ratios of blue galaxies (i.e., while blue galaxies ies have systematically brighter outer profiles than green and have bright disks stars do not domired galaxies. In addition, the massσ profiles highlight that the 2 due to young stars,σthose σgv = 0.10 GV = 0.14 GV = 0.11 nate the total stellar mass). Despite the similar outer mass promain difference in (R) between galaxies of different colors 7 files, it can be seen that< red galaxies is found in their inner regions (R. 1 kpc). At fixed mass, log M < 10.75have, on average, higher < log M < < log M < mass densities in the inner regions (R. a few kpc) than blue green and red galaxies have inner surface densities systematobjects. The 6lower-right panel shows that the SD profiles of ically larger than blue galaxies by about a factor of 2 3. As green and red galaxies are very similar at all radii. mentioned in Section 2.3, recently reported IMF variations 5 beyond a single mass and redshift bin to exwe now move would increase the difference in inner (R) between blue and amine the SB and SD profiles of all galaxies in the volumered galaxies. 4 Figure 8 presents the median i-band SB limited sample. Taking the view that galaxies evolve from blue to red at and SD profiles for galaxies in the sample, divided into the fixed mass, we are led to conclude that mass is building up in 3 same mass bins used in Figure 6. In each mass bin, galaxthe inner (bulge-dominated) regions as galaxies evolve. Moreies are divided into blue, green, and red galaxies based on over, most of this buildup occurs before the galaxy leaves the σgvconclusions = 0.09 σgv7= are 0.07esσGV = 0.07 NUV-r color.2 The drawn from Figure blue cloud. This last point is indicated by the observation that sentially the same for the whole sample. Beginning with the the SD profiles of green and red galaxies are nearly identi1.6is apparent is SB 2.0 cal 2.2in their 2.4 inner 1.6regions. 1.8 If, 2.0instead, 2.2 mass 2.4 buildup occurred SB profiles, what from2.2 the figure that the 1 as a galaxy transitioned from blue to red, we would profiles of green and red galaxies are remarkably similar at [km gradually log s ] 1 all radii in all mass bins. This suggests that green and red expect to see the green valley mass profiles take on values arevs. structurally very similar. The second notable asintermediate between bluegreen, and red galaxy profiles. guregalaxies 12. NUV-r in six stellar mass bins for the volume-limited sample. Errormore bars indicate median errors in 1 the for blue, and red galaxies in 1 pectbin. is the difference SB profiles thegreen, blueand and ThisThe expectation is strengthened by referring Figure ch mass Dotted gray lines between indicate thethe division between of blue, red galaxies. horizontal scatter in dex of the distribution in theback greento valley indicated at the bottom of each panel. The dotted red lines indicate the value of 1 above 80%mass of theslice, red galaxies are found in eachstellar mass bin. Though a green/red galaxies. In particular, the blue galaxies have signif6. which In each especially at lower masses where orrelation between NUV-r color isthis apparent, the surprising scatter and measurement in blue increasingly severe toward the lowerdistribution masses. 1 and 1 become icantly brighter outer regions. is not given the errorsthe cloud is well-populated, of galaxies Fang+13!23