Bulge Formation by the Coalescence of Giant Clumps in Primordial Disk Galaxies

By Bruce G. Elmegreen, Frédéric Bournaud, D. Elmegreen. 2008

305 citations recorded by the source corpus.

Gas-rich disks in the early universe are highly turbulent and have giant star-forming clumps. Models suggest that the clumps form by gravitational instabilities, and if they resist disruption by star formation, then they interact, lose angular momentum, and migrate to the center to form a bulge. Here we study the properties of the bulges formed by this mechanism. They are all thick, slowly rotating, and have a high Sersic index, like classical bulges. Their rapid formation should also give them relatively high α-element abundances. We consider fourteen low-resolution models and four high-resolution models, three of which have supernova feedback. All models have an active halo, stellar disk, and gaseous disk; three of the models have a pre-existing bulge, and three others have a cuspy dark matter halo. All show the same basic result except the one with the highest feedback, in which the clumps are quickly destroyed and the disk thickens too much. The coalescence of massive disk clumps in the center of a galaxy is like a major merger in terms of orbital mixing. It differs by leaving a bulge with no specific dark matter component, unlike the merger of individual galaxies. Normal supernova feedback has little effect, because the high turbulent speed in the gas produces tightly bound clumps. A variety of indirect observations support the model, including clumpy disks with young bulges at high redshift and bulges with relatively little dark matter.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/1aea08adc7436475068414564419291f1dcfdad0

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Star formation sustained by gas accretion (2014, background): “Alternatively, the external gas streams may fuel the disks with metal-poor gas, so that gas mass builds up developing starbursts through internal gravitational instabilities (e.g., Noguchi 1999; Elmegreen et al. 2008; Bournaud & Elmegreen 2009).”
BULGE AND CLUMP EVOLUTION IN HUBBLE ULTRA DEEP FIELD CLUMP CLUSTERS, CHAINS AND SPIRAL GALAXIES (2008, methodology): “This process forms a bulge and exponential disk within several orbit times, or ∼ 1 Gyr for a galaxy such as the Milky Way (Noguchi 1999; Immeli et al. 2004a, 2004b; Carollo et al. 2007; Bournaud et al. 2007; Bournaud et al. 2008; Elmegreen et al. 2008a, 2008b).”
Chemical similarities between Galactic bulge and local thick disk red giants: O, Na, Mg, Al, Si, Ca, and Ti (2010, background): “Recently, Elmegreen et al. (2008) have shown that bulges formed by coalescence of giant clumps can have properties of both classical and pseudo-bulges, because secular evolution can take place in a very short timescale (< 1 Gyr).”
Physical Models of Galaxy Formation in a Cosmological Framework (2014, background): “If these clumps survive and migrate to the galaxy center, they may form a classical bulge (Bournaud et al. 2011, Dekel et al. 2009, Elmegreen et al. 2008).”
Disc formation and the origin of clumpy galaxies at high redshift (2009, background): “This scenario is an extension of the disc fragmentation scenario proposed by B07 and Elmegreen et al. (2008), although here studied more consistently within the current cosmological framework, and more specifically related to cosmological accretion.”
BLACK HOLE GROWTH AND ACTIVE GALACTIC NUCLEI OBSCURATION BY INSTABILITY-DRIVEN INFLOWS IN HIGH-REDSHIFT DISK GALAXIES FED BY COLD STREAMS (2011, background): “These BHs can grow inside classical bulges (Elmegreen et al. 2008b).”
FORMATION OF MASSIVE GALAXIES AT HIGH REDSHIFT: COLD STREAMS, CLUMPY DISKS, AND COMPACT SPHEROIDS (2009, background): “In many cases there is also a significant central bulge, of a somewhat older stellar population than in the disk clumps (Genzel et al. 2008), but somewhat younger than in regular spirals (Elmegreen et al. 2008c).”
THE SINS SURVEY OF z ∼ 2 GALAXY KINEMATICS: PROPERTIES OF THE GIANT STAR-FORMING CLUMPS (2010, background): “…10tdyn(Rdisk) < 0.5 Gyr, (1) where they may form a central bulge and a remnant thick disk (Noguchi 1999; Immeli et al. 2004a, 2004b; Förster Schreiber et al. 2006; Genzel et al. 2006, 2008; Elmegreen et al. 2008; Carollo et al. 2007; Dekel et al. 2009a; Bournaud et al. 2009; Ceverino et al. 2010).”
The rising star formation histories of distant galaxies and implications for gas accretion with time (2010, background): “The existence of gaseous disks likely requires that distant galaxies form stars at a quasi-steady pace, and not in short periods of enhanced star formation such as merger-driven starbursts (see, Elmegreen et al. 2008; Bournaud et al. 2008; Dekel et al. 2009; Renzini 2009).”
A DIVERSITY OF PROGENITORS AND HISTORIES FOR ISOLATED SPIRAL GALAXIES (2012, background): “…Murray et al. 2010), where they participate in building the bulge, thus providing another channel for bulge formation at high redshift (Noguchi 1999; Immeli et al. 2004; Bournaud et al. 2007a; Genzel et al. 2008; Elmegreen et al. 2008; Agertz et al. 2009; Dekel et al. 2009a; Ceverino et al. 2010).”
KILOPARSEC-SCALE DUST DISKS IN HIGH-REDSHIFT LUMINOUS SUBMILLIMETER GALAXIES (2016, background): “…suggest that secular processes within star– forming galaxies are driving their gas and stars into the central regions, building up exponential disks and massive bulges without the need for major mergers (e.g., Elmegreen et al. 2008; Genzel et al. 2008; Dekel et al. 2009, 2013; Bournaud 2016).”
Cuspy No More: How Outflows Affect the Central Dark Matter and Baryon Distribution in Lambda CDM Galaxies (2012, background): “…2002 RAS, MNRAS 000, 1–12 local radiation play an important role in determining the structure of the ISM and where SF can occur (Kennicutt 1998; Elmegreen et al. 2008; Krumholz & McKee 2005; Bigiel et al. 2008; Gnedin et al. 2009; Feldmann et al. 2011; Narayanan et al. 2011).”
Chemical tagging with APOGEE: Discovery of a large population of N-rich stars in the inner Galaxy (2016, background): “(i) In situ GC origin: Bournaud et al. (2007) and Elmegreen et al. (2008) proposed that the Galactic bulge was formed by the coallescence of giant clumps hosted by turbulent disks at high redshift (see review by Bournaud 2015).”
Alpha element abundances and gradients in the Milky Way bulge from FLAMES-GIRAFFE spectra of 650 K giants (2011, background): “Such clumpy and turbulent rotating disks are in fact observed in galaxies around z ∼ 2 (Elmegreen et al. 2008).”
THE DEPENDENCE OF QUENCHING UPON THE INNER STRUCTURE OF GALAXIES AT 0.5 ⩽ z < 0.8 IN THE DEEP2/AEGIS SURVEY (2012, methodology): “To alleviate these issues, we also consider other models, specifically, violent disk instability (Noguchi 1999; Elmegreen et al. 2008; Dekel et al. 2009), secular evolution (Kormendy & Kennicutt 2004), morphological quenching (Martig et al. 2009), and halo quenching (Silk 1977; Rees & Ostriker…”