Goddard Space Center

Goddard, MD, United States

Goddard Space Center

Goddard, MD, United States
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Van Der Wel A.,Max Planck Institute for Astronomy | Franx M.,Leiden University | Van Dokkum P.G.,Yale University | Skelton R.E.,South African Astronomical Observatory | And 28 more authors.
Astrophysical Journal | Year: 2014

Spectroscopic+photometric redshifts, stellar mass estimates, and rest-frame colors from the 3D-HST survey are combined with structural parameter measurements from CANDELS imaging to determine the galaxy size-mass distribution over the redshift range 0 < z < 3. Separating early- and late-type galaxies on the basis of star-formation activity, we confirm that early-type galaxies are on average smaller than late-type galaxies at all redshifts, and we find a significantly different rate of average size evolution at fixed galaxy mass, with fast evolution for the early-type population, R eff(1 + z) -1.48, and moderate evolution for the late-type population, R eff(1 + z)-0.75. The large sample size and dynamic range in both galaxy mass and redshift, in combination with the high fidelity of our measurements due to the extensive use of spectroscopic data, not only fortify previous results but also enable us to probe beyond simple average galaxy size measurements. At all redshifts the slope of the size-mass relation is shallow, , for late-type galaxies with stellar mass >3 × 109 M , and steep, , for early-type galaxies with stellar mass >2 × 1010 M . The intrinsic scatter is ≲0.2 dex for all galaxy types and redshifts. For late-type galaxies, the logarithmic size distribution is not symmetric but is skewed toward small sizes: at all redshifts and masses, a tail of small late-type galaxies exists that overlaps in size with the early-type galaxy population. The number density of massive (∼1011 M ), compact (R eff < 2 kpc) early-type galaxies increases from z = 3 to z = 1.5-2 and then strongly decreases at later cosmic times. © 2014. The American Astronomical Society. All rights reserved..


Kriek M.,University of California at Berkeley | Shapley A.E.,University of California at Los Angeles | Reddy N.A.,University of California at Riverside | Siana B.,University of California at Riverside | And 21 more authors.
Astrophysical Journal, Supplement Series | Year: 2015

In this paper we present the MOSFIRE Deep Evolution Field (MOSDEF) survey. The MOSDEF survey aims to obtain moderate-resolution (R = 3000-3650) rest-frame optical spectra (∼3700-7000 ) for ∼1500 galaxies at in three well-studied CANDELS fields: AEGIS, COSMOS, and GOODS-N. Targets are selected in three redshift intervals:, down to fixed (F160W) magnitudes of 24.0, 24.5, and 25.0, respectively, using the photometric and spectroscopic catalogs from the 3D-HST survey. We target both strong nebular emission lines (e.g., [O ii], Hβ, [O iii], H, [N ii], and [S ii]) and stellar continuum and absorption features (e.g., Balmer lines, Ca-ii H and K, Mgb, 4000 break). Here we present an overview of our survey, the observational strategy, the data reduction and analysis, and the sample characteristics based on spectra obtained during the first 24 nights. To date, we have completed 21 masks, obtaining spectra for 591 galaxies. For ∼80% of the targets we derive a robust redshift from either emission or absorption lines. In addition, we confirm 55 additional galaxies, which were serendipitously detected. The MOSDEF galaxy sample includes unobscured star-forming, dusty star-forming, and quiescent galaxies and spans a wide range in stellar mass () and star formation rate. The spectroscopically confirmed sample is roughly representative of an H-band limited galaxy sample at these redshifts. With its large sample size, broad diversity in galaxy properties, and wealth of available ancillary data, MOSDEF will transform our understanding of the stellar, gaseous, metal, dust, and black hole content of galaxies during the time when the universe was most active. © 2015. The American Astronomical Society. All rights reserved.


Van Der Wel A.,Max Planck Institute for Astronomy | Chang Y.-Y.,Max Planck Institute for Astronomy | Bell E.F.,University of Michigan | Holden B.P.,University of California at Santa Cruz | And 17 more authors.
Astrophysical Journal Letters | Year: 2014

We determine the intrinsic, three-dimensional shape distribution of star-forming galaxies at 0 < z < 2.5, as inferred from their observed projected axis ratios. In the present-day universe, star-forming galaxies of all masses 109-1011 M are predominantly thin, nearly oblate disks, in line with previous studies. We now extend this to higher redshifts, and find that among massive galaxies (M * > 1010 M disks are the most common geometric shape at all z ≲ 2. Lower-mass galaxies at z > 1 possess a broad range of geometric shapes: the fraction of elongated (prolate) galaxies increases toward higher redshifts and lower masses. Galaxies with stellar mass 109 M (1010 M) are a mix of roughly equal numbers of elongated and disk galaxies at z1 (z2). This suggests that galaxies in this mass range do not yet have disks that are sustained over many orbital periods, implying that galaxies with present-day stellar mass comparable to that of the Milky Way typically first formed such sustained stellar disks at redshift z1.5-2. Combined with constraints on the evolution of the star formation rate density and the distribution of star formation over galaxies with different masses, our findings imply that, averaged over cosmic time, the majority of stars formed in disks. © 2014. The American Astronomical Society. All rights reserved..


News Article | November 3, 2016
Site: news.yahoo.com

The next roundtrip flight you take from New York to Europe means you will personally contribute to the melting of 32 square feet of Arctic sea ice by September in a given year, according to a groundbreaking new study published Thursday. Or to put it another way, in a given year, the average American melts about 538 square feet of Arctic sea ice at the end of the summer melt season. The study, published in the journal Science this week, for the first time makes the link between individual actions in lower latitudes with the rapid, expansive changes taking place in the Arctic. SEE ALSO: 'Not enough ice for a gin and tonic:' two weeks in the Northwest Passage The new study is particularly resonant given that sea ice extent declined to its second-lowest level on record this year, and a sailing vessel managed to traverse the Northwest Passage without spotting any large chunks of sea ice at all. The U.S.-German team of researchers responsible for the study found that about 3 square meters of summer sea ice disappear in the Arctic for every metric ton of carbon dioxide added to the atmosphere. They then used that relationship to translate the ice loss into the carbon footprint of our everyday activities, be it flying or taking a long, 2,500-mile road trip via car. The study also explores the linear relationship between the amount of carbon dioxide added to the atmosphere over time and long-term changes in the average monthly sea ice area in September, which is when the ice typically reaches its annual minimum. The researchers found that this type of relationship holds up best when studying the observational record of sea ice area from 1953 through 2015, and show it is likely to continue to hold in the future. "We hope that this study will allow people to more intuitively grasp the mere fact that Arctic sea ice does not disappear because of some large-scale, anonymous action, but simply because of our little day-to-day activities," said study co-author Dirk Notz, a senior researcher at the Max Planck Institute for Meteorology in Hamburg, Germany, in an email to Mashable. "Hence, the loss of Arctic sea ice really is our shared responsibility, which then also implies that we have the means to slow down and eventually stop that ice loss, for example by following the Paris agreement," he said. The Arctic’s summer ice cover has shrunk by more than half during the past four decades, with a recent acceleration of this trend. The Arctic is warming at about twice the average rate of the rest of the world. Arctic sea ice loss is also suspected to be altering the jet stream and leading to extreme weather events in the U.S. and Europe in recent years. Climate models show that Arctic sea ice may be completely lost by mid-century unless stringent emissions cuts are enacted. More specifically, the study found that additional cumulative greenhouse gas emissions have to remain under 1,000 billion tons (or 1,000 gigatons) of carbon dioxide in order to keep some Arctic summer sea ice cover. In other words, our carbon bank account has 1,000 billion tons in it, and if we go over that, one of the many penalties we'll pay is in the form of a seasonally ice-free Arctic Ocean. Losing it completely would alter the way of life for the people who call the Arctic home, as well as pose existential threats to iconic species such as the polar bear and walrus.  Currently, the world is on course to put far more carbon dioxide into the air than 1,000 billion tons, considering we are emitting between 30 and 40 billion tons of carbon dioxide per year. This means an ice-free Arctic Ocean during the summer months is possible as early as 2045, according to the study. Some countries better than others The researchers produced a map showing which countries' citizens are destroying the most sea ice, based on carbon emissions per capita.  Residents of the U.S. and the European Union, not surprisingly, were found to bear most of the responsibility when compared to growing developing nations like China and India, where emissions per capita are still lower.  For example, based on 2013 emissions data, the average American was responsible for destroying about 10 times the amount of sea ice compared to the average citizen of India.  "We also wanted to provide a more tangible way for policy makers to understand our contributions to sea ice loss, which is where the map idea came from," said co-author Julienne Stroeve, a senior researcher at the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado, and a professor at the University College London. Need to stay below 2-degree limit  The study found that global warming would need to be held below 2 degrees Celsius, or 3.6 degrees Fahrenheit, compared to preindustrial levels by 2100 in order to have a good chance of maintaining some ice cover during the summer in the Far North.   Ice seen in the Northwest Passage in 2016. Walt Meier, who studies sea ice at NASA's Goddard Space Center and was not involved in the new study, said it is interesting work that contradicts the hypothesis that reinforcing or runaway feedback loops in the Arctic would cause a sudden acceleration of ice loss over time. "This paper is further evidence against a tipping point and towards a more linear response. Of course, this is over the long-term — the paper looks at 30-year running means. Over the shorter term (several years), there is a lot of variability," Meier said in an email.  He added that the linkage of specific carbon dioxide emissions to ice loss amounts is a new, albeit "highly simplified" visualization of how human-caused climate change is reshaping the Arctic.  "Where this tying of [greenhouse gas emissions] to ice loss is probably most impactful is on policymakers and the general public," he said. The study comes at a fortuitous time, since the next round of U.N. climate negotiations, during which the possibility of making more stringent emissions cuts will be on the agenda, begin in Marrakech, Morocco on Nov. 7.


Van Dokkum P.G.,Yale University | Bezanson R.,University of Arizona | Van Der Wel A.,Max Planck Institute for Astronomy | Nelson E.J.,Yale University | And 14 more authors.
Astrophysical Journal | Year: 2014

The dense interiors of massive galaxies are among the most intriguing environments in the universe. In this paper,we ask when these dense cores were formed and determine how galaxies gradually assembled around them. We select galaxies that have a stellar mass >3 × 1010 M inside r = 1 kpc out to z = 2.5, using the 3D-HST survey and data at low redshift. Remarkably, the number density of galaxies with dense cores appears to have decreased from z = 2.5 to the present. This decrease is probably mostly due to stellar mass loss and the resulting adiabatic expansion, with some contribution from merging. We infer that dense cores were mostly formed at z > 2.5, consistent with their largely quiescent stellar populations. While the cores appear to form early, the galaxies in which they reside show strong evolution: their total masses increase by a factor of 2-3 from z = 2.5 to z = 0 and their effective radii increase by a factor of 5-6. As a result, the contribution of dense cores to the total mass of the galaxies in which they reside decreases from 50% at z = 2.5 to 15% at z = 0. Because of their early formation, the contribution of dense cores to the total stellar mass budget of the universe is a strong function of redshift. The stars in cores with M 1 kpc > 3 × 1010 M ̇make up 0.1% of the stellar mass density of the universe today but 10%-20% at z 2, depending on their initial mass function. The formation of these cores required the conversion of 1011 M of gas into stars within 1 kpc, while preventing significant star formation at larger radii. © 2014. The American Astronomical Society. All rights reserved..


PubMed | Goddard Space Center, Leiden University, Max Planck Institute for Astronomy, South African Astronomical Observatory and 5 more.
Type: Journal Article | Journal: Nature | Year: 2014

Most massive galaxies are thought to have formed their dense stellar cores in early cosmic epochs. Previous studies have found galaxies with high gas velocity dispersions or small apparent sizes, but so far no objects have been identified with both the stellar structure and the gas dynamics of a forming core. Here we report a candidate core in the process of formation 11 billion years ago, at redshift z = 2.3. This galaxy, GOODS-N-774, has a stellar mass of 100 billion solar masses, a half-light radius of 1.0 kiloparsecs and a star formation rate of solar masses per year. The star-forming gas has a velocity dispersion of 317 30 kilometres per second. This is similar to the stellar velocity dispersions of the putative descendants of GOODS-N-774, which are compact quiescent galaxies at z 2 (refs 8-11) and giant elliptical galaxies in the nearby Universe. Galaxies such as GOODS-N-774 seem to be rare; however, from the star formation rate and size of this galaxy we infer that many star-forming cores may be heavily obscured, and could be missed in optical and near-infrared surveys.


Van Dokkum P.G.,Yale University | Nelson E.J.,Yale University | Franx M.,Leiden University | Oesch P.,Yale University | And 12 more authors.
Astrophysical Journal | Year: 2015

In this paper we study a key phase in the formation of massive galaxies: the transition of star-forming galaxies into massive (Mstars ∼ 1011Mo), compact (re ∼ 1 kpc) quiescent galaxies, which takes place from z ∼ 3 to z ∼ 1.5. We use HST grism redshifts and extensive photometry in all five 3D-HST/CANDELS fields, more than doubling the area used previously for such studies, and combine these data with Keck MOSFIRE and NIRSPEC spectroscopy. We first confirm that a population of massive, compact, star-forming galaxies exists at z ≳ 2, using K-band spectroscopy of 25 of these objects at 2.0 < z < 2.5. They have a median [N ii]/Hα ratio of 0.6, are highly obscured with SFR(tot)/SFR(Hα) ∼10, and have a large range of observed line widths. We infer from the kinematics and spatial distribution of Hα that the galaxies have rotating disks of ionized gas that are a factor of ∼2 more extended than the stellar distribution. By combining measurements of individual galaxies, we find that the kinematics are consistent with a nearly Keplerian fall-off from Vrot ∼ 500 km s-1 at 1 kpc to Vrot ∼ 250 km s-1 at 7 kpc, and that the total mass out to this radius is dominated by the dense stellar component. Next, we study the size and mass evolution of the progenitors of compact massive galaxies. Even though individual galaxies may have had complex histories with periods of compaction and mergers, we show that the population of progenitors likely followed a simple inside-out growth track in the size-mass plane of Δ log re ∼ 0.3 Δ log Mstars. This mode of growth gradually increases the stellar mass within a fixed physical radius, and galaxies quench when they reach a stellar density or velocity dispersion threshold. As shown in other studies, the mode of growth changes after quenching, as dry mergers take the galaxies on a relatively steep track in the size-mass plane. © 2015. The American Astronomical Society. All rights reserved.


Van Dokkum P.G.,Yale University | Leja J.,Yale University | Nelson E.J.,Yale University | Patel S.,Leiden University | And 15 more authors.
Astrophysical Journal Letters | Year: 2013

Galaxies with the mass of the Milky Way dominate the stellar mass density of the universe but it is uncertain how and when they were assembled. Here we study progenitors of these galaxies out to z = 2.5, using data from the 3D-HST and CANDELS Treasury surveys. We find that galaxies with present-day stellar masses of log (M) ≈ 10.7 built ∼90% of their stellar mass since z = 2.5, with most of the star formation occurring before z = 1. In marked contrast to the assembly history of massive elliptical galaxies, mass growth is not limited to large radii: the mass in the central 2 kpc of the galaxies increased by a factor of between z = 2.5 and z = 1. We therefore rule out simple models in which bulges were fully assembled at high redshift and disks gradually formed around them. Instead, bulges (and black holes) likely formed in lockstep with disks, through bar instabilities, migration, or other processes. We find that after z = 1 the growth in the central regions gradually stopped and the disk continued to be built up, consistent with recent studies of the gas distributions in z ∼ 1 galaxies and the properties of many spiral galaxies today. © 2013. The American Astronomical Society. All rights reserved.


Patel S.G.,Leiden University | Fumagalli M.,Leiden University | Franx M.,Leiden University | Van Dokkum P.G.,Yale University | And 13 more authors.
Astrophysical Journal | Year: 2013

We follow the structural evolution of star-forming galaxies (SFGs) like the Milky Way by selecting progenitors to z ̃ 1.3 based on the stellar mass growth inferred from the evolution of the star-forming sequence. We select our sample from the 3D-HST survey, which utilizes spectroscopy from the HST/WFC3 G141 near-IR grism and enables precise redshift measurements for our sample of SFGs. Structural properties are obtained from Sérsic profile fits to CANDELS WFC3 imaging. The progenitors of z = 0 SFGs with stellar mass M = 1010.5 M * are typically half as massive at z ̃ 1. This late-time stellar mass growth is consistent with recent studies that employ abundance matching techniques. The descendant SFGs at z ̃ 0 have grown in half-light radius by a factor of ̃1.4 since z ̃ 1. The half-light radius grows with stellar mass as re ∝M 0.29. While most of the stellar mass is clearly assembling at large radii, the mass surface density profiles reveal ongoing mass growth also in the central regions where bulges and pseudobulges are common features in present day late-type galaxies. Some portion of this growth in the central regions is due to star formation as recent observations of Hα maps for SFGs at z ̃ 1 are found to be extended but centrally peaked. Connecting our lookback study with galactic archeology, we find the stellar mass surface density at R = 8 kpc to have increased by a factor of ̃2 since z ̃ 1, in good agreement with measurements derived for the solar neighborhood of the Milky Way. © 2013. The American Astronomical Society. All rights reserved.


Leja J.,Yale University | Van Dokkum P.G.,Yale University | Momcheva I.,Yale University | Brammer G.,European Southern Observatory | And 11 more authors.
Astrophysical Journal Letters | Year: 2013

We present Keck/MOSFIRE K-band spectroscopy of the first mass-selected sample of galaxies at z ∼ 2.3. Targets are selected from the 3D-Hubble Space Telescope Treasury survey. The six detected galaxies have a mean [N II]λ6584/Hα ratio of 0.27 ± 0.01, with a small standard deviation of 0.05. This mean value is similar to that of UV-selected galaxies of the same mass. The mean gas-phase oxygen abundance inferred from the [N II]/Hα ratios depends on the calibration method, and ranges from 12+log(O/H)gas = 8.57 for the Pettini & Pagel calibration to 12+log(O/H)gas = 8.87 for the Maiolino et al. calibration. Measurements of the stellar oxygen abundance in nearby quiescent galaxies with the same number density indicate 12+log(O/H)stars = 8.95, similar to the gas-phase abundances of the z ∼ 2.3 galaxies if the Maiolino et al. calibration is used. This suggests that these high-redshift star forming galaxies may be progenitors of today's massive early-type galaxies. The main uncertainties are the absolute calibration of the gas-phase oxygen abundance and the incompleteness of the z ∼ 2.3 sample: the galaxies with detected Hα tend to be larger and have higher star formation rates than the galaxies without detected Hα, and we may still be missing the most dust-obscured progenitors. © 2013. The American Astronomical Society. All rights reserved.

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