Formation of elongated galaxies with low masses at high redshift

We report the identification of elongated (triaxial or prolate) galaxies in cosmological simulations at $z\simeq2$. These are preferentially low-mass galaxies ($M_s \le 10^{9.5} \ M_\odot$), residing in dark-matter (DM) haloes with strongly elongated inner parts, a common feature of high-redshift DM haloes in the $\Lambda$CDM cosmology. Feedback slows formation of stars at the centres of these halos, so that a dominant and prolate DM distribution gives rise to galaxies elongated along the DM major axis. As galaxies grow in stellar mass, stars dominate the total mass within the galaxy half-mass radius, making stars and DM rounder and more oblate. A large population of elongated galaxies produces a very asymmetric distribution of projected axis ratios, as observed in high-z galaxy surveys. This indicates that the majority of the galaxies at high redshifts are not discs or spheroids but rather galaxies with elongated morphologies.

[1]  Guillermo Barro,et al.  Compaction and quenching of high-z galaxies in cosmological simulations: blue and red nuggets , 2014, 1412.4783.

[2]  A. Dekel,et al.  Early formation of massive, compact, spheroidal galaxies with classical profiles by violent disc instability or mergers , 2014, 1409.2622.

[3]  Christopher E. Moody,et al.  Diverse structural evolution at z > 1 in cosmologically simulated galaxies , 2014, 1409.1583.

[4]  K. Alatalo,et al.  The ATLAS 3D project - XXIV. The intrinsic shape distribution of early-type galaxies , 2014, 1408.1099.

[5]  A. Dekel,et al.  Four phases of angular-momentum buildup in high-z galaxies: from cosmic-web streams through an extended ring to disc and bulge , 2014, 1407.7129.

[6]  H. Rix,et al.  GEOMETRY OF STAR-FORMING GALAXIES FROM SDSS, 3D-HST, AND CANDELS , 2014, 1407.4233.

[7]  Christopher E. Moody,et al.  Star formation and clumps in cosmological galaxy simulations with radiation pressure feedback , 2014, 1405.5266.

[8]  A. Dekel,et al.  Wet Disc Contraction to Galactic Blue Nuggets and Quenching to Red Nuggets , 2013, 1310.1074.

[9]  A. Dekel,et al.  Radiative feedback and the low efficiency of galaxy formation in low-mass haloes at high redshift , 2013, 1307.0943.

[10]  M. Carollo,et al.  PSEUDOBULGE FORMATION AS A DYNAMICAL RATHER THAN A SECULAR PROCESS , 2012, 1211.1713.

[11]  K. Ohta,et al.  INTRINSIC SHAPE OF STAR-FORMING BzK GALAXIES. II. REST-FRAME ULTRAVIOLET AND OPTICAL STRUCTURES IN GOODS-SOUTH AND SXDS , 2012, 1210.2750.

[12]  R. Wechsler,et al.  THE AVERAGE STAR FORMATION HISTORIES OF GALAXIES IN DARK MATTER HALOS FROM z = 0–8 , 2012, 1207.6105.

[13]  S. White,et al.  Galactic star formation and accretion histories from matching galaxies to dark matter haloes , 2012, 1205.5807.

[14]  Shaun Cole,et al.  The shapes and alignments of dark matter halos , 2011, 1111.5616.

[15]  A. Kravtsov,et al.  THE IMPACT OF BARYON PHYSICS ON THE STRUCTURE OF HIGH-REDSHIFT GALAXIES , 2011, 1108.5384.

[16]  Ue-Li Pen,et al.  Can 21-cm observations discriminate between high-mass and low-mass galaxies as reionization sources? , 2011, 1107.4772.

[17]  David R. Law,et al.  AN HST/WFC3-IR MORPHOLOGICAL SURVEY OF GALAXIES AT z = 1.5–3.6. I. SURVEY DESCRIPTION AND MORPHOLOGICAL PROPERTIES OF STAR-FORMING GALAXIES , 2011, 1107.3137.

[18]  A. Dekel,et al.  Rotational support of giant clumps in high-z disc galaxies , 2011, 1106.5587.

[19]  A. Helmi,et al.  The shape of dark matter haloes in the Aquarius simulations: evolution and memory , 2011, 1104.1566.

[20]  Lucio Mayer,et al.  FORMING REALISTIC LATE-TYPE SPIRALS IN A ΛCDM UNIVERSE: THE ERIS SIMULATION , 2011, 1103.6030.

[21]  Edward John Routh,et al.  The elementary part of A treatise on the dynamics of a system of rigid bodies , 2009 .

[22]  A. Dekel,et al.  High-redshift clumpy discs and bulges in cosmological simulations , 2009, 0907.3271.

[23]  James Binney,et al.  Galactic Dynamics: Second Edition , 2008 .

[24]  Frank C. van den Bosch,et al.  Concentration, spin and shape of dark matter haloes as a function of the cosmological model: WMAP1, WMAP3 and WMAP5 results , 2008, 0805.1926.

[25]  Princeton University.,et al.  The shapes of galaxies in the Sloan Digital Sky Survey , 2008, 0802.0877.

[26]  A. Klypin,et al.  THE ROLE OF STELLAR FEEDBACK IN THE FORMATION OF GALAXIES , 2007, 0712.3285.

[27]  J. Read,et al.  The Causes of Halo Shape Changes Induced by Cooling Baryons: Disks versus Substructures , 2007, 0707.0737.

[28]  Astronomy,et al.  The spin and shape of dark matter haloes in the Millennium simulation of a Λ cold dark matter universe , 2006, astro-ph/0608607.

[29]  B. Moore,et al.  Concentration, spin and shape of dark matter haloes: Scatter and the dependence on mass and environment , 2006, astro-ph/0608157.

[30]  S. M. Fall,et al.  The Morphological Diversities among Star-forming Galaxies at High Redshifts in the Great Observatories Origins Deep Survey , 2006, astro-ph/0606696.

[31]  Risa H. Wechsler,et al.  The shape of dark matter haloes : dependence on mass, redshift, radius and formation , 2005, astro-ph/0508497.

[32]  A. Kravtsov.  On the Origin of the Global Schmidt Law of Star Formation , 2003, astro-ph/0303240.

[33]  Y. Jing,et al.  Triaxial Modeling of Halo Density Profiles with High-Resolution N-Body Simulations , 2002, astro-ph/0202064.

[34]  A. Dekel,et al.  A Universal Angular Momentum Profile for Galactic Halos , 2000, astro-ph/0011001.

[35]  S. White,et al.  The formation of galactic discs , 1997, astro-ph/9707093.

[36]  A. Klypin,et al.  Adaptive Refinement Tree: A New High-Resolution N-Body Code for Cosmological Simulations , 1997, astro-ph/9701195.

[37]  G. Illingworth,et al.  The ordered nature of elliptical galaxies - Implications for their intrinsic angular momenta and shapes , 1991 .

[38]  S. Faber,et al.  Contraction of Dark Matter Galactic Halos Due to Baryonic Infall , 1986 .

[39]  S. M. Fall,et al.  Formation and rotation of disc galaxies with haloes , 1980 .

[40]  H. F. Erguson,et al.  THE MORPHOLOGICAL DIVERSITIES AMONG STAR-FORMING GALAXIES AT HIGH REDSHIFTS IN THE GREAT OBSERVATORIES ORIGINS DEEP SURVEY , 2008 .