Quantifying Surface Brightness Quantifying SB profiles - PDF document

Quantifying Surface Brightness Quantifying SB profiles Non-Parametric Parametric � CSB : � 0 � Effective parameters: � The extrapolated central � e , r e r e surface brightness from � � � � Defined as the surface 2 � rI ( r ) dr = 2 2 � rI ( r ) dr the fit to the galaxy disk. 0 brightness level ( � e ) 0 at the half-light radius µ e � µ ( r e ) (r e ) Non-Parametric � Effective SB : � e � Concentration: C 28 � � C 28 = 5log r � Defined as the surface 80 � The log of the ratio of � � brightness level ( � e ) radii which contain 80% r � � at the half-light radius. 20 and 20% of the total flux Lecture 3 Padova Lecture Series 2007 53 Lecture 3 Padova Lecture Series 2007 54 A few words about concentration Properties of C 28 C 28 � 5log( r 80 / r 20 ) For 300 � r 80 and r 20 are the radii at 80% and 20% of total light Virgo � C 28 is wavelength dependent (use reddest bands), galaxies; but non-parametric (unlike e.g. B/T) C 28,i McDonald, � C 28 is independent of absolute calibration (unlike R e , µ e ) Courteau � Pure disks have C 28 =2.8 but Freeman Type II disks & Tully can have C 28 <2.8 (2008) � Concentration is slightly degraded (lower values) by seeing; the effect is strongest (a few %) at higher C 28 � We measured C 28 from SDSS i -band images for 32 spirals, 12 ellipticals, and 33 SO’s in our sample. C 28,H log r e,H Lecture 3 Padova Lecture Series 2007 55 Lecture 3 Padova Lecture Series 2007 56 Photometric data Sersic Light Profiles Freeman (1970) introduced two types of disk � 1/ n � � � � � � R I bulge ( R ) = I 0 exp � � � � light profiles: r � � � � � � 0 MacArthur, Courteau & Holtzman (2003) Lecture 3 Padova Lecture Series 2007 57 Lecture 3 Padova Lecture Series 2007 60

Bulge/Disk Scale Length Ratios Caveats in BD decompositions (taking B/D decompositions at face value) The entire formulation of the B/D decomposition • structural coupling presented so far relies on the assumption of between bulge and continuity of the disk below the bulge and the disk ( � r e /h � = 0.22 ± 0.09 ) bulge below the disk. • independent of The structure of bulge and disk relies on detailed wavelength kinematics of bulge and disk stars (tomorrow’s lecture). • consistent with scenarios of bulge Consider M31 for example... formation via secular evolution MacArthur et al. (2003) Lecture 3 Padova Lecture Series 2007 65 Lecture 3 Padova Lecture Series 2007 70 Virgo Cluster Galaxies Scaling Relations Ellipticals + dE,dS McDonald et al. (2008) Spirals + Irregulars Bender et al.(1992) Lecture 3 Padova Lecture Series 2007 76 Lecture 3 Padova Lecture Series 2007 77 Thick Disks � Most disk galaxies have additional, thick, disk (Yoachim/Dalcanton) � Modest mass fraction, but increases below v c ~120 km s -1 � Some counter-rotate: � external origin � Heavier counter-rotating disks seen in S0s (Kannappan) Hint of a thick disk � [ � /Fe] vs [Fe/H] in MW thick disk � it cannot have Two pure disk galaxies formed by accretion of small stellar lumps (Venn) � Origin in gas-rich merger (Sommer-Larsen) NGC 4244 NGC 5907 vdK&S Lecture 3 Padova Lecture Series 2007 79 Lecture 3 Padova Lecture Series 2007 80

DISK ! TRUNCATIONS M33 surface brightness Light profile profile (Ferguson etal 2003) Sharp decrease in SB NGC 4656: small bulge and prominent thick disk beyond 5 disk scale Star lengths. counts vdK&S (reaches V~31 mag arcsec -2 !) Lecture 3 Padova Lecture Series 2007 81 Lecture 3 Padova Lecture Series 2007 82 DISK ! TRUNCATIONS Disk truncations What is the origin of this disk truncation? Common and seen more easily in edge-on rather than in face-on galaxies NGC 300* surface brightness profile Kregel etal (2002): NGC 300 M33 (Bland-Hawthorne R max /h R = 3.6 ± 0.6 etal 2005) for 34 edge-on disk galaxies Light profile Exponential profile Perez (2004) finds extends to 10 disk scale Star similar results at lengths without a counts 0.6 <z <1 truncation! Star counts * Similar to M33 Kregel etal 2002 Lecture 3 Padova Lecture Series 2007 83 Lecture 3 Padova Lecture Series 2007 84 Interpretations of disk truncations • The radius associated with the maximum angular momentum • lifted with the addition of infrared photometry of the disk baryons in the proto-galaxy -- unlikely -- many disks have HI extending far beyond the truncation radius • The radius to which the disk has grown today -- unlikely -- The outer disks may be younger but still typically many Gyr old (eg Bell & de Jong 2000; Ferguson et al 2003; MacArthur et al. 2004). In some galaxies (eg M83, Milky Way), star formation continues in the outer disk but there is an underlying old component. • The radius where the gas density goes below the critical value for star formation (Kennicutt 1989) - star formation regulated by disk stability -- likely (van den Bosch 2001) Bruzual & Charlot models Lecture 3 Padova Lecture Series 2007 85 Lecture 3 Padova Lecture Series 2007 86

Photometric data Freeman (1970) introduced two types of disk light profiles: MacArthur, Courteau & Holtzman (2003) Lecture 3 Padova Lecture Series 2007 87 Lecture 3 Padova Lecture Series 2007 88 Age-metallicity gradients from colors in disk galaxies � Compare colour gradients with stellar population models Disks grow � Determine main drivers of SFH as a function of galaxy structural inside-out; parameters (e.g. surface density, total mass) Age gradients stronger than metallicity gradients; upturn at large radii for early-type systems. MacArthur etal (2004) MacArthur, Courteau, Bell, & Holtzman (2004) Lecture 3 Padova Lecture Series 2007 89 Lecture 3 Padova Lecture Series 2007 91 Galaxy Spectra • set of 21 spectral absorption line indices to monitor the �� strength of spectral features in Relative Flux stars and composite systems (galaxies) • 11 strongest & most reliable indices calibrated as a function of colour, surface g, and Z for semi-empirical population models (e.g Worthey 1994, Vazdekis 1999, Maraston et al. 2003, Bruzual & Charlot 2003) Wavelength (Å) Worthey & Ottaviani 1997 Lecture 3 Padova Lecture Series 2007 94 Lecture 3 Padova Lecture Series 2007 95