Draft version October 8, 2019 Typeset using LATEX twocolumn style in AASTeX62 The Carnegie-Irvine Galaxy Survey. VIII. Demographics of Bulges along the Hubble Sequence Hua Gao (高f),1, 2 Luis C. Ho,2, 1 Aaron J. Barth,3 and Zhao-Yu Li4 1Department of Astronomy, School of Physics, Peking University, Beijing 100871, China 2Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China 3Department of Physics and Astronomy, University of California at Irvine, 4129 Frederick Reines Hall, Irvine, CA 92697-4575, USA 4Department of Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China ABSTRACT We present multi-component decomposition of high-quality R-band images of 320 disk galaxies from the Carnegie-Irvine Galaxy Survey. In addition to bulges and disks, we successfully model nuclei, bars, disk breaks, nuclear/inner lenses, and inner rings. Our modeling strategy treats nuclear rings and nuclear bars as part of the bulge component, while other features such as spiral arms, outer lenses, and outer rings are omitted from the fits because they are not crucial for accurate bulge measurements. The error budget of bulge parameters includes the uncertainties from sky level measurements and model assumptions. Comparison with multi-component decomposition from the Spitzer Survey of Stellar Structure in Galaxies reveals broad agreement for the majority of the overlapping galaxies, but for a considerable fraction of galaxies there are significant differences in bulge parameters caused by different strategies in model construction. We confirm that on average bulge prominence decreases from early to late-type disk galaxies, although the large scatter of bulge-to-total ratios in each morphological bin limits the application of Hubble type as an accurate predictor of bulge-to-total ratio. In contrast with previous studies claiming that barred galaxies host weaker bulges, we find that barred and unbarred spiral galaxies have similar bulge prominence. Keywords: galaxies: bulges | galaxies: elliptical and lenticular, cD | galaxies: photometry | galax- ies: spiral | galaxies: structure 1. INTRODUCTION and mergers (Toomre 1977; Bournaud 2016). However, Motivated by the wealth of information stored in the in recent decades, there has been increasing appreci- morphological structures of galaxies, Ho et al.(2011) ation that bulges actually constitute a heterogeneous initiated the Carnegie-Irvine Galaxy Survey (CGS) to population. Bulges in late-type spirals show a younger investigate the optical photometric properties of 605 stellar population, more flattened stellar light distri- bright galaxies in the southern hemisphere. Detailed bution, and more rotation-dominated kinematics com- analysis of the high-quality CGS images has yielded sig- pared with bulges in early-type disks (e.g., Wyse et al. nificant insights into many aspects of the Hubble se- 1997; Kormendy & Kennicutt 2004; Fisher & Drory quence of galaxies, including the nature of disk breaks 2008; Fisher et al. 2009; Laurikainen et al. 2016). These (Li et al. 2011), the formation history of ellipticals dichotomies in bulge properties suggest distinct forma- (Huang et al. 2013a,b, 2016), the bar buckling phe- tion physics. In addition to violent processes, secular arXiv:1901.03195v2 [astro-ph.GA] 5 Oct 2019 nomenon (Li et al. 2017), the nature of S0s (Gao et al. evolution, facilitated by nonaxisymmetries in the galaxy 2018), and the origin of spiral arms (Yu & Ho 2018a,b). potential, is able to transport gas with low angular mo- Galaxy bulges are, of course, one of the fundamen- mentum to galaxy centers to build up bulges that re- tal, defining characteristics of the Hubble sequence, and sembles disks rather than merger-built ellipticals (e.g., hence constitute a central theme of this long-term pro- Kormendy & Kennicutt 2004; Athanassoula 2005; Sell- gram. wood 2014; Tonini et al. 2016). The disky bulges formed As ellipticals and bulges bear resemblance in many as- in this manner are commonly referred to in the litera- pects of their observational properties (e.g., Faber 1977; ture as pseudobulges, to distinguish them from classical Gott 1977; Renzini 1999), they were once thought to bulges. have similar origin: both form out of rapid, violent pro- Despite the importance of bulges in defining the Hub- cesses, such as gravitational collapse (Eggen et al. 1962) ble sequence and their rich formation physics, robust 2 quantitative measurements of their structural parame- Section4. In Section5, we study how B=T is distributed ters are yet to be achieved for large, well-defined sam- along the Hubble Sequence. Section6 summarizes the ples. One-dimensional (1D) fitting of galaxy surface paper. brightness profiles (e.g., Kormendy 1977a,b; Burstein 1979) and two-dimensional (2D) fitting of galaxy im- 2. SAMPLE AND DATA ages (e.g., Shaw & Gilmore 1989; Byun & Freeman 1995; The CGS sample is defined by BT ≤ 12:9 mag and de Jong 1996a) are the two widely employed paramet- δ < 0◦, without any reference to morphology, size, or ric techniques. Non-parametric techniques are less of- environment. Details of the observations and data re- ten used because of the difficulty of applying them to duction are given in Ho et al.(2011) and Li et al.(2011), nearly face-on cases (e.g., Kent 1986; Capaccioli et al. and will not be repeated here. We focus on the images 1987; Scorza & Bender 1990; Simien & Michard 1990). taken in the R band because this filter is less sensitive In terms of parametric fitting, 2D methods are superior to dust extinction and young stars; we avoid the I band because they preserve the maximum amount of spatial because its point-spread function (PSF) suffers from the information on morpholically distinct components and \red halo" effect (see Appendix A of Huang et al. 2013a). because they conserve flux during the convolution pro- The majority of the R-band images are of high quality: cess (Byun & Freeman 1995; de Jong 1996a; see Sec- the median seeing is 100: 01, the median surface bright- tion 1 of Gao & Ho 2017 for a review of the methods). ness depth is 26.4 mag arcsec−2, and the field-of-view of Nevertheless, both 1D and 2D methods suffer from the 8:09 × 8:09 is large enough to ensure robust sky determi- uncertainties introduced by the non-uniqueness of input nation for most of the galaxies. surface brightness models. The sample analyzed in this paper is an extension to In order to clarify which morphological features are the sample of S0s presented in Gao et al.(2018). We most essential in 2D model construction when the pri- add 304 non-edge-on spirals selected with morphologi- mary intent is to obtain robust bulge parameters, Gao cal type index 0 < T ≤ 9:5 and inclination angle i ≤ 70◦. & Ho(2017) selected a representative sample from CGS During the course of performing the decomposition, we that covers a sufficiently wide range of morphological ended up removing 46 galaxies for a variety of reasons: features (bars, lenses, rings, and spiral arms) and ex- two galaxies do not have R-band images; one galaxy is plored the impact of modeling the secondary morpho- edge-on with a razor-thin disk; two galaxies do not have logical features. They showed that modeling nuclear photometric calibration; two galaxies are highly dust- and inner lenses/rings and disk breaks has considerable attenuated and are located in fields extremely crowded impact on bulge parameters, whereas outer lenses/rings with stars; ten galaxies are highly irregular; three galax- and spiral arms have a negligible effect. For example, ies do not yield reasonable fits; and 26 galaxies are bul- failure to model disk breaks or lenses introduces errors geless. This leaves 258 spirals with measurable bulges, that can be as large as ∼ 50% in bulge-to-total ratio which, when combined with the 62 S0s, results in a final (B=T ) for barred galaxies (see also Kim et al. 2014). sample of 320 disk galaxies. The bulgeless galaxies are This important effect is generally ignored in many de- of particular interest (e.g., Kormendy et al. 2010; Fisher composition studies (e.g., Simard et al. 2011; Meert et al. & Drory 2011), but they are beyond the scope of this 2015; Salo et al. 2015; but see Laurikainen et al. 2005; paper. We list them in AppendixA for future consid- Kim et al. 2016; M´endez-Abreuet al. 2017). These eration. A brief description of the main morphological alarming uncertainties compel us to measure a new set of features of each successfully decomposed galaxy is given bulge parameters for nearby galaxies, derived in a con- in AppendixB. sistent manner following the optimal strategy defined in Figure1 summarizes the basic parameters of the suc- Gao & Ho(2017). cessfully decomposed sample of 320 galaxies. The stellar Toward this end, Gao et al.(2018) successfully de- masses (M?) for 313 galaxies were derived from the total composed 62 CGS S0 galaxies. This paper extends our Ks magnitudes compiled in Ho et al.(2011) and mass- previous work and presents a comprehensive catalog of to-light ratios following Equation (9) in Kormendy & bulge parameters for 320 non-edge-on disk galaxies in Ho(2013): CGS. Definition of the sample and description of the data are given in Section2. We closely follow and ex- log (M=L)Ks = 1:055(B − V ) − 0:9402; (1) pand the strategy in Gao & Ho(2017) to decompose the using (B − V ) colors from CGS (Li et al. 2011). The galaxies, as detailed in Section3. We compare the CGS galaxies in the sample are nearby (median D = bulge parameters with those from the Spitzer Survey of L 26:1 Mpc) and massive [median log (M =M ) = 10:57]. Stellar Structure in Galaxies (S4G; Sheth et al. 2010) in ? Note that some of the S0s have morphological type 3 indices T < −3 due to the inclusion of misclassified models are significant, especially for CGS galaxies that ellipticals (Gao et al.