The origin of dwarf galaxies, cold dark matter, and biased galaxy formation

“Numerous studies have invoked feedback from star formation or an ionizing background to darken dwarfs by expelling gas and inhibiting star formation in low mass halos (Dekel & Silk 1986; Quinn, Katz & Efstathiou 1996).”

“Star-formation (Dekel & Silk 1986, Babul & Rees 1992, De Young and Heckman 1994) and ram-pressure stripping (Faber & Lin 1983, van den Bergh 1994c) have been proposed as means of removing gas from dwarfs in the inner Galactic halo.”

“This is only weakly dependent on the gas fraction, density or metallicity (Dekel & Silk 1986, eq.”

“, by photoionization and stellar feedback.(31,32,8) The early presence of low-SFR galaxies(25,26) requires quenching of SFR also at the massive end, perhaps due to gravitational heating by destructive streams.”

“In low-mass systems, feedback from supernova-driven winds can be very effective as winds can easily expel large amounts of gas from haloes with low escape velocities (e.g. Larson 1974; Dekel & Silk 1986; Oppenheimer & Davé 2008; Puchwein & Springel 2012).”

“…models of galaxy formation within a CDM framework recognized this “overcooling problem”, and suggested that energy generated by supernova explosions could heat gas and perhaps blow it out of galaxies, making star formation inefficient (Dekel & Silk 1986, White & Frenk 1991, White & Rees 1978).”

“Photoionization and supernova-driven winds serve to limit cooling and star formation in low-mass halos (Dekel & Silk 1986).”

“For larger mass haloes (up to Vvir 150– 200 km s−1), the standard assumption is that winds driven by massive stars and supernovae (SNe) are able to heat and expel gas, resulting in low baryon fractions in small-mass haloes (White & Rees 1978; Dekel & Silk 1986; White & Frenk 1991).”

“For example, the satellites may be dark simply because baryons were removed long ago through supernova-driven winds (Dekel & Silk 1986; Mac Low & Ferrara 1999).”

“Examples of such are baryonic feedback effects on dark matter (Dekel & Silk 1986) or non-gravitational interactions between dark matter particles (Spergel & Steinhardt 1999).”

“…ago that an apparently more successful way of explaining both the regular relations and the dichotomies is to assume some form of feedback process (Dekel & Silk 1986), which must be abl to stop the star formation and the chemical evolution by heating and expelling the gas from the galaxy…”

“…considerations indicate that feedback effects are likely to be important in galaxies as large as ∼ 1011M⊙ and may thus affect the shock stability (e.g. Dekel & Silk 1986; Dekel & Woo 2003, and references therein), it has proven difficult for numerical simulations to reproduce such effects in any…”

“Following the general argu- c© 0000 RAS, MNRAS 000, 000–000 ments of Dekel & Silk (1986), we now calculate the rate at which gas can escape from the disk: ṁrh, disk = 2frh,disk ǫ̇SN 〈v2 esc, disk〉 , (9) and from the halo (same expression with 〈v2esc, halo〉).”

“This is in contrast to the conventional picture in the galaxy formation literature (Dekel & Silk 1986).”

“Dekel & Silk (1986) evaluated the maximum energy fed into the interstellar gas by supernovae, taking into account the radiative loses, ESN ≃ ǫ ν Ṁ∗ trad, where Ṁ∗ refers to the SFR in each clump, ǫ is the energy released by a typical supernova (∼ 1051erg), and ν is the number of supernovae per…”

“These aspects have been investigated in a number of theoretical papers (Larson 1974 ; Dekel & Silk 1986 ; Silk, Wyse, & Shields 1987 ; Vader 1986, 1987 ; Ferrara & Tolstoy 1999, hereafter FT) in both local and cosmological contexts.”

“Most importantly, hydrodynamic simulations of galaxy formation usually include some form of stellar feedback (e.g., Dekel & Silk 1986; Navarro & White 1993; Mihos & Hernquist 1994; Gerritsen & Icke 1997; Thacker & Couchman 2000; Kay et al. 2002; Kawata & Gibson 2003; Sommer-Larsen et al. 2003;…”

“In contrast to earlier work, both analytical (e.g., Larson 1974, Dekel & Silk 1986, Scannapieco et al. 2002, Furlanetto & Loeb 2003) and numerical (e.g., Mori et al. 2002, Thacker et al. 2002, Wada & Venkatesan 2003), their focus is on the minihalos that are the sites for the formation of the very…”

“Possible explanations include galaxy harrassment (González-García et al. 2005) and rapid expansion after baryonic blowout (Dekel & Silk 1986; Hensler et al. 2004).”

“The popular model of Dekel and Silk (1986) combines the notion of lower amplitude peaks in the hierarchical model with the use of stellar winds or supernovae to reshape the small galaxies that have low binding energy by expelling their gas (Larson 1974, Vader 1986).”

“Theoretical models generally produce a somewhat weaker inverse relationship with mass, e.g. the momentum-driven wind model of Murray et al (2005) has λ ∝ m-1/3, whereas an energy-driven wind (e.g. Dekel and Silk 1986) has λ ∝ m-2/3.”

“This solution is similar in some ways to the idea that supernova feedback ejects gas from low-mass halos (Dekel & Silk 1986), but it offers a natural explanation for why some satellite galaxies at each circular velocity survive, while most are too dim to be seen.”

“…tight observed coupling between galaxy spheroidal components and central active galactic nuclei (AGN) are not yet fully understood, although it has long been recognized that the formation mechanisms of SMBHs (e.g. Silk & Rees 1998) and stars (e.g. Dekel & Silk 1986) are most likely selfregulating.”

“…star formation is therefore expected to occur, and the subsequent negative feedback due to supernova explosions would prevent the assembly of large quantities of gas in the center of the shallow dark matter (DM) potential well that characterizes the first dwarf galaxies (e.g., Dekel & Silk 1986).”

“…for this discrepancy are well studied and it has been argued that feedback from SNII is important for low mass systems (e.g. Larson 1974; Dekel & Silk 1986; Guo et al. 2010a) and feedback from supermassive black holes dominates for high mass systems (Croton et al. 2006; Di Matteo et al.…”

“It is possible that the high SN galaxies (the Fornax dSph with SN ∼ 29 is an extreme example) simply represent those in which stellar feedback during the first major starburst was very effective (e.g., Dekel & Silk 1986).”

“The relation can be explained by the retention of metals in the galaxies’ gravitational potential wells (e.g., Dekel & Silk 1986).”

“If even a relatively small amount of the energy from supernovae can couple to the interstellar medium of a galaxy, it can remove gas from shallow gravitational potential wells and thereby regulate star formation in low-mass systems (Larson 1974; Dekel & Silk 1986).”

“The reason for this failure in the early models is that star formation continues unchecked in massive haloes where supernova feedback is insufficient (Dekel & Silk 1986).”

“Best et al. 2005; Croton et al. 2006) and winds driven by supernovae are an example of ejective feedback (e.g. Dekel & Silk 1986; Springel & Hernquist 2003).”

“…work (White & Rees 1978) it was already noted that at high-redshift gas has to be prevented from excessive cooling into overly dense regions - possibly by feedback from massive stars to avoid the overproduction of condensed baryonic matter (Dekel & Silk 1986, Larson 1974, Navarro & Benz 1991).”

“Our finding in fact agrees with the proposed common origin of dwarf spheroidal and low-mass spiral galaxies and irregulars (Kormendy 1985; Dekel & Silk 1986), but also shows an empirical continuity between dwarf spheroidals and a subset of the ellipticals family.”

“One reason why such objects are prevented from forming is that primordial clouds of mass are readily disrupted by supernova-driven[109 M _winds (Dekel & Silk 1986).”

“This “star formation feedback” is widely thought to be a key ingredient in the evolution of starforming galaxies (Dekel & Silk 1986; Kauffmann et al. 1993; Finlator & Davé 2008; Efstathiou 2000; Bouché et al. 2010; Dutton et al. 2010).”

“It can explain the absence of young galaxies with very low mass, Vrot<∼ 10 − 20 km s−1 , after reionization (Barkana & Loeb 1999), the slope of the galaxy luminosity function (Dekel & Silk 1986; Dekel & Woo 2003; Benson et al. 2003), and the mass-metallicity relation among galaxies (Larson 1974).”

“In galaxies less massive than L*, winds generated by stellar feedback are thought to suppress star formation and eject gas from galaxies into the CGM and IGM (Larson 1974; White & Rees 1978; Dekel & Silk 1986).”

“…M⊙, the galaxy formation efficiency is reduced, consistent with the fact that feedback can reduce the star formation efficiency in small haloes, while cooling becomes less effective in more massive haloes (e.g., White & Rees 1978; Dekel & Silk 1986; van den Bosch 2002; Benson et al. 2000).”

“…effect of feedback on the structure of galaxies and the efficiency of SF were originally motivated by the discrepancy between the observed number of dwarf galaxies and the much higher number density of small DM halos predicted by CDM models (Dekel & Silk 1986; Moore et al. 1998; Bower et al. 2006).”

“Following Dekel & Silk (1986) and Dekel & Woo (2003), this critical baryonic mass is given by Mb;crit ¼ 2:0 ; 1010 vd;crit 100 km s 1 3 1þ z 3:2 2”

“Understanding such galactic feedback processes is crucial for developing a complete theory of galaxy formation and evolution (Dekel & Silk 1986), as observations such as the shallow faint-end slope of the galaxy stellar mass function (Cole et al. 2001) versus the halo mass function (Jenkins et al.…”

“…be due either to photo-heating associated with the fresh UV background after reionization (e.g. Thoul & Weinberg 1996; Quinn et al. 1996; Barkana & Loeb 1999; Gnedin 2000; Dijkstra et al. 2004), or to SN feedback (e.g. Dekel & Silk 1986; Dutton & van den Bosch 2009; Oppenheimer & Davé 2008) 10.”

“In turn, theorists have suggested a suite of physical processes to suppress star formation and/or expel gas from the galaxies (Dekel & Silk 1986; Somerville & Primack 1999; Oppenheimer et al. 2010).”

“…the compaction, may involve gas starvation by rapid consumption into stars, the associated gas loss via outflows driven by stellar feedback (e.g. Dekel & Silk 1986; Murray, Quataert & Thompson 2005) or AGN feedback (e.g. Ciotti & Ostriker 2007; Cattaneo et al. 2009, for a review), and possibly…”

“The canonical explanation is that this turnover reflects the efficiency of metal ejection from galaxies because the gravitational potential wells of galaxies at and above this mass scale are too deep for supernova-driven winds to escape (Dekel & Silk 1986; Dekel & Woo 2003; Tremonti et al. 2004).”

“However, one would expectthat in these various scenarios, those few galaxies within voids should have di erent physical propertiesfrom galaxies in the denser regions (Dekel & Silk 1986; Ho man, Silk, & Wyse 1992; Brainerd & Villumsen1992).”

“The most common form of feedback used in hierarchical models is the ejection of cold gas from a galactic disk by a supernova driven wind (e.g. Larson 1974; Dekel & Silk 1986).”

“Second, our conclusion implies that the star formation rate in galaxies cannot solely be determined by feedback produced by massive stars (supernovae, stellar winds) as hypothesized by several authors (Dekel & Silk 1986; Murray et al. 2010; Dobbs et al. 2011; Hopkins et al. 2011).”

“The common thought is that low-mass galaxies lose their metals more easily because winds can escape from these galaxies’ shallower potential wells (e.g. Dekel & Silk 1986).”

“These processes are canonically believed to govern the mass-metallicity relation (e.g. Dekel & Silk 1986; Tremonti et al. 2004); the phrase “metals can more easily escape from the shallower potential wells of small galaxies” is oft-repeated.”

“…challenging even after 30 years of theoretical studies (e.g., Mathews & Baker 1971; Larson 1974; Ozernoi & Chernomordik 1978; Ostriker & Cowie 1981; Dekel & Silk 1986; Ikeuchi & Ostriker 1986; Voit 1996; Nath & Trentham 1997; Mac Low & Ferrara 1999; Aguirre et al. 2001; Cen & Bryan 2001; Madau,…”

“These effects are expected to be stronger at lower masses and redshift, where the potential wells are shallower (Dekel & Silk 1986).”

“These processes have re-shaped their dark and baryonic components throughout the galaxies’ lifetimes (e.g., Dekel & Silk 1986; Efstathiou 1992; Mac Low & Ferrara 1999; Bullock et al. 2000; Mayer et al. 2001; Governato et al. 2010; Brooks et al. 2013; Kazantzidis et al. 2013).”

“…in order to account for the inefficient star formation witnessed for both the low-mass dwarf galaxies and for the massive ellipticals at the center of groups and clusters, feedback from Supernovae (SNe) (Dekel & Silk 1986) and from Active Galactic Nuclei (AGN) (Silk & Rees 1998) respectively.”

“A leading candidate for such a mechanism is galactic winds (e.g. Dekel & Silk 1986).”

“The rather dramatic failure of our constant wind scenario is suprising in light of the apparent success of the simple analytical models presented by Dekel & Silk (1986) and Dekel & Woo (2003).”

“It is widely thought that the low baryon masses of galaxies are due to galactic winds driven by stellar feedback at the faint end of the stellar mass function (Dekel & Silk 1986; Efstathiou 2000) and by the active galactic nuclei (AGN) and the bright end (Silk & Rees 1998; Benson et al. 2003).”

“We note, however, that there are many studies of feedback in shallow potential wells (see, e.g., Dekel & Silk 1986; Silk et al. 1987; Read et al. 2006a; Mayer et al. 2007) which discuss the clear importance of energy balance in driving gas loss and in expanding extant stellar systems.”

“In return, the more luminous galaxies may undergo stronger enrichment and, due to their deeper potential wells, also have an improved ability to retain the metals (e.g., Dekel & Silk 1986).”

“Several studies of how this feedback may physically operate can be found in the literature (Dekel & Silk 1986; Mac Low & Ferrara 1999; Goodwin, Pearce & Thomas 2000).”

“Our fiducial model for supernova feedback is similar to the model used in most semi-analytic models based on Dekel & Silk (1986).”

“It has long been recognized that the formation processes of supermassive black-holes (BHs) and stars may be selfregulating (Dekel & Silk 1986; Silk & Rees 1998), since the amount of energy released by quasars and stars can exceed the binding energy of the gas clouds in which they are born.”

“Low mass galaxies have shallow potential wells so they tend to lose a significant fraction of their gas and metals, while massive galaxies have potential wells deep enough to prevent material from escaping the galaxy (e.g. Dekel & Silk 1986).”

“…these faint galaxies could be the result of cosmic reionization and stellar feedback quenching gas accretion and star formation in low-mass haloes (Dekel & Silk 1986; Thoul & Weinberg 1996; Bullock, Kravtsov & Weinberg 2000; Ferrara & Tolstoy 2000; Benson et al. 2002a,b; Somerville 2002; Susa &…”

“These various mechanisms are believed to be responsible for SF regulation in dwarf galaxies (Dekel & Silk 1986), and they contribute collectively to roughly a couple of 1051 erg of energy injection into the surrounding ISM, for an average 10 M massive star and for a standard stellar initial mass…”

“Dekel & Silk (1986) showed that supernova feedback can eject gas from galaxies with virial velocities up to 100 km s−1.”

“Supernova blow-out likely plays a role in regulating star formation if CDM is the correct theory (Dekel & Silk 1986; Kauffmann et al. 1993; Cole et al. 1994; Somerville & Primack 1999); however, supernova winds do not naturally suggest a sharp discrepancy at ∼ 30 km s−1, nor do they explain why…”

“The turnover in the MZR at high masses has typically been thought to reflect the transition to a regime where outflows can no longer escape the galaxy (Dekel & Silk 1986; Tremonti et al. 2004).”

“Star formation of low-mass galaxies is assumed to be halted via stellar feedback, for example, stellar winds or supernova explosions that heat/eject gas (Larson 1974; Dekel & Silk 1986; Leitherer et al. 1999).”

“Dekel & Silk (1986) predicted the scaling relation, L / Z 2:7, for dwarf galaxies formed and embedded within dark matter halos, although their model is less applicable to dwarf galaxies which have undergone a low and constant level of star formation over a Hubble time.”

“Feedback describes the efficiency with which massive stars reheat the surrounding interstellar medium (ISM), and it is thought to have a particularly strong impact on the star formation history of low-mass galaxies (Dekel & Silk 1986 ; Larson 1974).”