THE TRUE DURATIONS OF STARBURSTS:HUBBLE SPACE TELESCOPEOBSERVATIONS OF THREE NEARBY DWARF STARBURST GALAXIES

Abstract

The duration of a starburst is a fundamental parameter affecting the evolution of galaxies yet, to date, observational constraints on the durations of starbursts are not well established. Here we study the recent star formation histories of three nearby dwarf galaxies to rigorously quantify the duration of their starburst events using a uniform and consistent approach. We find that the bursts range from ∼200 to ∼400 Myr in duration resolving the tension between the shorter timescales often derived observationally with the longer timescales derived from dynamical arguments. If these three starbursts are typical of starbursts in dwarf galaxies, then the short timescales (3-10 Myr) associated with starbursts in previous studies are best understood as "flickering" events which are simply small components of the larger starburst. In this sample of three nearby dwarfs, the bursts are not localized events. All three systems show bursting levels of star formation in regions of both high and low stellar density. The enhanced star formation moves around the galaxy during the bursts and covers a large fraction of the area of the galaxy. These massive, long-duration bursts can significantly affect the structure, dynamics, and chemical evolution of the host galaxy and can be the progenitors of "superwinds" that drive much of the recently chemically enriched material from the galaxy into the intergalactic medium.

Hidden starbursts and active galactic nuclei at 0 < z < 4 from theHerschel-VVDS-CFHTLS-D1 field: Inferences on coevolution and feedback

“…For the typical strength of the starburst in the ULIRG sample, ∼350 M yr −1 , these are stellar masses that are built up in only 50-100 Myr, a time roughly equal to the typical length of the peak of star-formation in a starburst event (Swinbank et al 2006;Hopkins et al 2008Hopkins et al , 2012McQuinn et al 2009;Wild et al 2010) and roughly equal to the age since the beginning of the burst derived in the previous section. This scenario does not, however, work for even for the least massive LIRGs in our sample as a burst at the mean SFR of the LIRG sample (∼50 M yr −1 ) would have to be sustained at a constant level for the previous 500 Myr−Gyr to build up the necessary stellar mass in the observed burst.…”

“…In some cases, star formation is thought to proceed in a sporadic manner, particularly at high redshifts, with undisturbed, low-level, continuous star formation being the exception in galaxies rather than the primary mechanism of building stellar Article published by EDP Sciences A90, page 1 of 39 mass (e.g., Kolatt et al 1999;Bell et al 2005;Papovich et al 2005Papovich et al , 2006Nichols et al 2012;Pacifici et al 2013). Violent episodes of star formation, known as starbursts, can dramatically alter the stellar mass of galaxies with sufficient gas reservoirs during the relatively short period that constitutes the lifetime of a starburst (typically ∼100-500 Myr; Swinbank et al 2006;Hopkins et al 2008;McQuinn et al 2009McQuinn et al , 2010bWild et al 2010; though perhaps up to ∼700 Myr for particular populations, e.g., Lapi et al 2011;Gruppioni et al 2013). Such events contribute significantly to the global star formation rate (SFR) of galaxies both in the high-redshift universe (e.g., Somerville et al 2001;Chapman et al 2005;Erb et al 2006;Magnelli et al 2009) and locally (e.g., Brinchmann et al 2004;Kauffmann et al 2004; Lee et al 2006Lee et al , 2009 and are furthermore thought to be a typical phase of evolution undergone by massive quiescent galaxies observed at low redshifts early in their formation history (e.g., Juneau et al 2005;Hickox et al 2012).…”

Star Forming Dwarf Galaxies

“…The marks indicate starburst durations derived from other groups using other data. Among these are the results from McQuinn et al [109] (right pointer), Lee et al [90] (dot) and various results arriving at short durations discussed in McQuinn et al [107] (left pointer).…”

“…Therefore it may be well motivated to redefine the criterion. Thus, in their study of nearby SFGDs, McQuinn et al [107,109] accordingly consider only the latest 6 Gyr when they discuss starburst properties, b=b/ < b > (0−6Gyr) . They also prefer to lower the condition further and consider the galaxy to be in a starburst condition if this modified b is > 2.…”

The supergiant shell with triggered star formation in the dwarf irregular galaxy IC 2574: neutral and ionized gas kinematics

“…Weisz et al (2009a) showed that the holes in the Holmberg II galaxy contain multiple stellar generations and could indeed be formed from the energy input of these stars. Today it is clear that high star-formation rates can be maintained for a much longer time period than previously believed: dwarf galaxies are characterized by the ability to sustain a high star-formation efficiency over several hundred Myr, and even up to 1000 Myr in some cases (McQuinn et al 2009(McQuinn et al , 2010a, with local short starbursts occurring during this period. Such long periods of intense star formation provide enough energy from stellar winds and supernova explosions to drive the formation of giant cavities and supergiant shells (see e.g.…”