Spectral Analysis and Galaxy Properties Tinggui Wang USTC, Hefei
What can a galaxy spectrum tell?3 components star-light, emission lines, occasionally, interstellar absorption lines
Star-light mass, age, metallicity distribution of stellar populations,, extinction and kinematics of starsEmission lines SFR/level of nuclear activity metallicity and physical conditions of gas kinematic of gasInterstellar Absorption Lines kinematic of ISM
Star-lightage, metallicity distribution of stellar populations,, average extinction and kinematics of stars
Fitting galaxy spectra with templates a subset SSPs Kauffmann et al. 2003; Panter et al. 2009; CidFernandes et al. 2005 Independent components of SSPs Lu et al. 2006proved to work effectively and efficiently for SDSS spectra, provided model SSPs are accuracy.
Input .vs. recovered stellar mass weighted age for IC methods. looks better if using light-weighted. Lu et al. 2006But different population synthesis models give substantial different results in some cases.
bigBOSS spectra: Higher spectral resolution and broader l coverage give more information, thus should lead to a better determination of stellar populations, also to resolved kinematics for dwarf galaxies Problems noisy: stacking analysis Lack of SSPs with a resolution R>5000 and a broad l- coverage , particularly in UV domain, using theoretical stellar atmosphere models
Emission lines SFR/level of nuclear activity (e.g., Baldwin Phillips and Terlervich 1982; Kauffmann etal 2003; Kewley et al. 2006) gas-phase abundancee.g., Shi et al. 2006; Kewley et al. 2008) gas density/pressure
We can extract information fairly successfully with Ha, Hb, [OIII], [NII], [SII], [OII] at low redshifts
This is more difficult @z>0.5, because AGN/SF classification relies on weak lines, particular problem in low s/n spectrumLack of good extinction indicator UV luminosity for SFR?
Interstellar Absorption LinesIn optical, NaI and CaII absorption lines, which trace thick gas, have been detected in starburst and reddened galaxies (Phillips 1993; Heckman et al. 2000; Rupke et al. 2002, 2005a, 2005b; Martin 2005, 2006).In ultraviolet, resonant absorption lines can provide much more sensitive probes of kinematics and physical state of interstellar gas.
At z>0.23, MgII, MgI absorption lines move into bigBOSS spectra, and other UV lines at larger redshifts.
Analysis of absorption lines are fairly straight forward, but in some cases subtraction of stellar absorption lines are essential. It also requires a reasonable S/N ratios (>10).
How can galaxy properties tell us about galaxy formation processes ? Galaxy formation and evolution are governed by many complicated physics processes, both internal and external environments.
Formation of DM halo, gas accretion, galaxy merger, tidal striping, bar instability, disk-bulge transformation, star formation, gas recycling, metal enrichments, galactic wind, nuclear activity, ..
Many of them are poorly understood.
to determine the role of different processes, compare observables with model prediction statisticallyCosmology simulation + SAM (or numerical simulations) with physics prescription model prediction of statistical properties of galaxies of today and in the past luminosity function mass-metallicity relation mass-age relation star formation history environment dependence of galactic properties many free parameters / uncertainties
studying rare populations can also tell a lot
Driver et al. 2007, The Millennium Galaxy CatalogueGalaxies split into red and blue sequences, Baldry et al. (2004)
also in other spectral (naturally) and structural parameters
Li et al. 2006 (also Mateus et al. 2006)Red dwarfs in different environment , Yang et al. 2008
what process quenches star formation process in red sequence? AGN (massive galaxies) feedback star-burst feed-back ram-pressure stripe of gas in a massive halo for dwarfs dynamic heating in cluster environment
Easy way to look at this problem is to study galaxies that has just switched off their star-formation process (E+A galaxies) or star-forming galaxy
Observed E+A galaxies at intermediate redshiftstellar populations may tell you how it turns offBetter age-resolution than red sequence galaxies-- Needs some tests
Tremonti et al. 2006Massive outflows at velocities up to 1000 km/s have been detected in E+A galaxies from its blue shifted interstellar absorption lines
Gas outflows have also been detected in star-forming galaxies with a mass ratio of 10-100 M yr (Weiner et al. 2009)
Relatively easy to be observed at moderate redshift: relative bright continuum due to its small M/L ratio strong absorption lines or emission lines probably meets current selection criteria for ELGs
Bright type 2 AGN @ intermediate zWhy are they interesting?X-ray, infared and optical survey s are effective to different populations of AGN complete census of cosmic black hole growth requires surveys at different wavebands probe galactic chemical enrichment history through type-2s narrow emission lines: the size of narrow line region is a substantial fraction of galactic bulge Host galaxies are relatively easily to be studied in type 2 than in type 1. how host galaxies change with redshift ?But, lack systematic survey of type 2 AGN beyond local universe.
metal abundance of NLRGroves, Heckman & Kauffmann (2004)Advantage:At intermediate z, CIV, CIII] SiIII CII and NeIV NeV may be all in the spectral coverage, thus providing rich diagnostics. Disadvantage:these lines are weaker than [OIII] Ha and [NII]. Line ratios sensitive to dust reddening
Peculiar abundance pattern in Q1321 High overall gas metallicity (Z~10) and overabundances of N and Si relative to C a fast chemical enriching process associated with a recent starburst, triggered by a recent galaxy merger.Wang et al. 2009Are there any other objects with a similar fast mass building process?
sparse in comparison with ELG some will be in the quasar regime on color-color diagram some may be in ELG sampleselection criteria to be defined surface density estimate
ConclusionWith broad wavelength coverage and high spectral resolution, bigBOSS gives rich information for bright galaxies, in order to extract these information:SSP @ R5000 and broad wavelength coveragecalibration of UV emission line metallicity indicators AGN/HII diagnostics with UV line ratios Despite statically comparison of model prediction and observations play key roles in the understanding important processes shaping the galaxy properties, we can learn a lot of about the formation of red-sequence and feedback processes though study of E+A and star forming galaxies at intermediate redshiftsType-2 AGN can be an interesting topic selection criteria need to be defined