Recent Results of the MPE Infrared/Submillimeter Group

 

Combined CO and dust scaling relations of depletion time and molecular gas fractions with cosmic time, specific star-formation rate, and stellar mass

February 2015

To measure the gas content of galaxies up to redshifts beyond 2 we apply two independent methods to large samples:  First, we use molecular gas masses inferred from CO emission in 500 star-forming galaxies (SFGs) , from the IRAM-COLDGASS, PHIBSS1/2, and other surveys. Second, we derive gas masses from Herschel far-IR dust measurements in 512 galaxy stacks over the same stellar mass/redshift range. The CO- and dust-based results agree remarkably well. We constrain the scaling relations of molecular gas depletion timescale (t depl) and gas to stellar mass ratio (M mol gas/M* ) of SFGs near the star formation "main-sequence" with redshift, specific star-formation rate (sSFR), and stellar mass (M* ). This suggests that the CO → H2 mass conversion factor varies little within ±0.6 dex of the main sequence (sSFR(ms, z, M *)), and less than 0.3 dex throughout this redshift range. This study builds on and strengthens the results of earlier work. We find that t depl scales as (1 + z)–0.3 × (sSFR/sSFR(ms, z, M *))–0.5, with little dependence on M *. The resulting steep redshift dependence of M mol gas/M * ≈ (1 + z)3 mirrors that of the sSFR and probably reflects the gas supply rate. The decreasing gas fractions at high M* are driven by the flattening of the SFR-M * relation. With these new relations it is now possible to determine M mol gas with an accuracy of ±0.1 dex in relative terms, and ±0.2 dex including systematic uncertainties.

<p>Depletion times (molecular gas mass / star formation rate) of z=0-2.3 galaxies, as derived from two independent methods and tracers: CO (blue) and dust (red). After removing a weak redshift dependence, depletion times are found to vary strongly with distance from the galaxy ‘main sequence’ (left). Removing also this dependence, depletion time on the main sequence is essentially independent of stellar mass (right).</p> Zoom Image

Depletion times (molecular gas mass / star formation rate) of z=0-2.3 galaxies, as derived from two independent methods and tracers: CO (blue) and dust (red). After removing a weak redshift dependence, depletion times are found to vary strongly with distance from the galaxy ‘main sequence’ (left). Removing also this dependence, depletion time on the main sequence is essentially independent of stellar mass (right).

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Evidence for widespread AGN-driven outflows in the most massive z~1-2 star-forming galaxies

November 2014

Adaptive optics assisted near-infrared integral field spectroscopy shows broad emission line components (white contours) superposed on the central region of massive z~2 star forming galaxies. The broad components extend over 2-3kpc and most likely indicate AGN-driven outflows. Zoom Image
Adaptive optics assisted near-infrared integral field spectroscopy shows broad emission line components (white contours) superposed on the central region of massive z~2 star forming galaxies. The broad components extend over 2-3kpc and most likely indicate AGN-driven outflows.
<p>Incidence of AGN in massive z~1-2 star-forming galaxies. All indicators suggest a rise with stellar mass, but the incidence of AGN-driven outflows (blue and red filled circles) is larger than traditional X-ray/optical/IR evidence for AGN in the same galaxies (stars) or similar evidence in large samples in popular deep fields (shaded bands).</p> Zoom Image

Incidence of AGN in massive z~1-2 star-forming galaxies. All indicators suggest a rise with stellar mass, but the incidence of AGN-driven outflows (blue and red filled circles) is larger than traditional X-ray/optical/IR evidence for AGN in the same galaxies (stars) or similar evidence in large samples in popular deep fields (shaded bands).

Very deep laser guide star assisted adaptive optics observations have allowed us to detect ubiquitous powerful nuclear outflows in massive (1011 MSun) z ∼ 2 star-forming galaxies, which are plausibly driven by an active galactic nucleus (AGN). The spectra in their central regions exhibit a broad component in Hα and forbidden [N II] and [S II] line emission, with typical velocity FWHM ∼ 1500 km s-1, high [NII]/Hα ratio ≈ 0.6, and intrinsic extent of 2–3 kpc. At larger radii, weaker and less wide broad components suggest star formation driven outflows. The high inferred nuclear mass outflow rates and frequent occurrence suggest that the nuclear outflows efficiently expel gas out of the centers of the galaxies with high duty cycles and may thus contribute to the process of star formation quenching in massive galaxies. Extending to a large sample observed without adaptive optics, we find that the incidence of the most massive galaxies with broad nuclear components is at least as large as that of AGNs identified by X-ray, optical, infrared, or radio indicators, as expected for rapidly varying AGN whose outflows are visible with larger duty cycle than X-ray or optical continuum. The mass loading of the nuclear outflows is near unity. Our findings provide compelling evidence for powerful, high-duty cycle, AGN-driven outflows near the Schechter mass, and acting across the peak of cosmic galaxy formation.

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Molecular gas, extinction, star formation and kinematics in the z=1.5 star forming galaxy EGS130111661

<p>In the top row, the molecular gas is shown as the backdrop image in color and the contours display the stellar light (from left to right: H band map, stellar mass, extinction corrected star formation rate). In the bottom row (center image), the backdrop shows the extinction and the white contours show the CO integrated flux map -- demonstrating how well the absorption seen in the rest-frame optical coincide with the CO emission. The high-resolution HST H-band maps show clumps of star formation, typical for galaxies at the peak of the cosmic star formation rate (see results from the high-redshift galaxy survey SINS)&nbsp;</p> Zoom Image

In the top row, the molecular gas is shown as the backdrop image in color and the contours display the stellar light (from left to right: H band map, stellar mass, extinction corrected star formation rate). In the bottom row (center image), the backdrop shows the extinction and the white contours show the CO integrated flux map -- demonstrating how well the absorption seen in the rest-frame optical coincide with the CO emission. The high-resolution HST H-band maps show clumps of star formation, typical for galaxies at the peak of the cosmic star formation rate (see results from the high-redshift galaxy survey SINS) 

<p>Comparison of CO (IRAM/PdB) and H-alpha (LBT/LUCI) data at the same resolution of FWHM 0.75". There is a remarkable agreement between the kinematics as derived from the molecular (traced by the sub-mm CO line) and ionized gas (traced by the H-alpha line) that shows that both tracers can be used equally well to study rotation curve and kinematics in high-redshift galaxies.</p> Zoom Image

Comparison of CO (IRAM/PdB) and H-alpha (LBT/LUCI) data at the same resolution of FWHM 0.75". There is a remarkable agreement between the kinematics as derived from the molecular (traced by the sub-mm CO line) and ionized gas (traced by the H-alpha line) that shows that both tracers can be used equally well to study rotation curve and kinematics in high-redshift galaxies.

As a follow-up to the high-redshift molecular gas survey PHIBBS (Tacconi et al. 2013; see news item below), a detailed study was performed of one of the most massive galaxies in this survey. For the study of the galaxy named EGS13011166, CO 3-2 line observations from the IRAM Plateau de Bure millimeter interferometer were combined with Large Binocular Telescope (LBT) LUCI observations of the H-alpha line in this galaxy, at matched spatial resolutions of 0.75 arcseconds. The galaxy was scanned perpendicular to the slit with LUCI to obtain spatially resolved spectra both along and perpendicular to the slit. Additionally, Hubble Space Telescope (HST) V-I-J-H band maps were used. Together these data allow to derive the stellar surface density and star formation rate, molecular gas surface density, optical extinction and gas kinematics.

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Discovery of a comet factory in a protoplanetary disk with ALMA

June 7, 2013

Using the new Atacama Large Millimeter/submillimeter Array (ALMA), a huge asymmetry has been found in the mm emission from a dust disk surrounding a young star. In contrast, the gas and micron-sized dust grains show a full ring. The data strongly suggests the presence of a dust trap around 60 AU from the star where dust particles can grow by clumping together. This is the first time that such a dust trap has been clearly observed and modelled. It solves a long-standing mystery about how dust particles in disks grow to larger sizes so that they can eventually form comets, planets and other rocky bodies. The images also demonstrate the excellent quality of ALMA data even at the highest frequencies (690 GHz, 0.45 mm, Band 9).

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The relation between molecular gas and star formation over half the cosmic time

April 16, 2013

<p>Dependence of normalized gas fraction on stellar mass. The normalisation is to the gas fraction of a galaxy with a stellar mass of 5 x 10^10 solar masses. Measurements at high redshift from the new PHIBSS survey are shown in black (here the redshift slice z=1-1.5 is used) and results from a local survey of molecular gas are shown as open squares (Saintonge et al. 2011a). The green shaded area gives an estimate of the gas fractions at high redshift corrected for incompleteness of the PHIBSS survey.</p> Zoom Image

Dependence of normalized gas fraction on stellar mass. The normalisation is to the gas fraction of a galaxy with a stellar mass of 5 x 10^10 solar masses. Measurements at high redshift from the new PHIBSS survey are shown in black (here the redshift slice z=1-1.5 is used) and results from a local survey of molecular gas are shown as open squares (Saintonge et al. 2011a). The green shaded area gives an estimate of the gas fractions at high redshift corrected for incompleteness of the PHIBSS survey.

<p>Specific star formation rate (sSFR) as a function of redshift. The big black and red points are entirely independent estimates of the sSFR over redshift: The black points use the molecular gas masses derived from the PHIBSS and other molecular gas surveys and derive the sSFR using stellar mass and the given dependency of gas depletion time with redshift (see label in plot). The red points, on the other hand, are the average values of direct measurements of the sSFR from imaging surveys (the individual measurements are shown underlying in gray).</p> Zoom Image

Specific star formation rate (sSFR) as a function of redshift. The big black and red points are entirely independent estimates of the sSFR over redshift: The black points use the molecular gas masses derived from the PHIBSS and other molecular gas surveys and derive the sSFR using stellar mass and the given dependency of gas depletion time with redshift (see label in plot). The red points, on the other hand, are the average values of direct measurements of the sSFR from imaging surveys (the individual measurements are shown underlying in gray).


An unprecedented survey of molecular gas at high redshift provides 52 CO detections in two redshift slices at a redshift z of about 1.2 and 2.2, with stellar masses (M_star) above 10^10.4 solar masses (M_sun) and star formation rates (SFR) above 10^1.5 M_sun per year. The survey is named PHIBSS which stands for the IRAM Plateau de Bure high-z blue sequence CO 3–2 survey of the molecular gas properties in massive, main-sequence star-forming galaxies (SFGs) near the cosmic star formation peak. Including a correction for the incomplete coverage of the M_star – SFR plane, and adopting a "Galactic" value for the CO–H2 conversion factor, average gas fractions are inferred of about 0.33 at z of about 1.2 and about 0.47 at z of about 2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the SFGs between redshifts of about 1 and 3 are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular-gas–star-formation relation for the z = 1–3 SFGs is near-linear, with a gas depletion timescale of about 0.7 Gyr; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between redshifts of about 0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M_star, gas fractions correlate strongly with the specific star formation rate (sSFR). The variation of sSFR between redshifts of 0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas.

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New observations on the Galactic Center gas cloud "G2"

September 12, 2012

New observations on the gas cloud "G2" falling towards the Galactic Center confirm its highly elliptical orbit, but with updated orbital parameters. With the new data, the cloud is now expected to come even closer -- the updated pericenter distance is 2200 Schwarzschild radii -- to the super-massive black hole at the center of our galaxy. While its origin is still unclear, its apocenter is near the inner edge of the disk of young stars. This supports speculations that the cloud, which has a mass of only about three earth masses, originated as a wind of one of these stars.

Data were recorded with the integral-field spectrograph SINFONI which produces data cubes containing a spectrum for each pixel. From this cube, data were extracted along a curved slit that matches the trajectory of the gas cloud and from a fit to the gas emission lines in the spectra, the velocity of the cloud was deduced for each position along the slit. The resulting plot shows at which velocity (x axis) the gas is moving depending on its position on the orbit (y axis) and color-coded for the epoch of observation (2008: red, 2011: blue, 2012: green). Apart from the cloud itself, a slow moving tail with velocities &lt; 1000 km/s is seen. While the observations clearly show that the gas cloud is being disrupted, up to now the evolution of the cloud can be fully explained with a simple test particle simulation without any hydrodynamical effects. Zoom Image
Data were recorded with the integral-field spectrograph SINFONI which produces data cubes containing a spectrum for each pixel. From this cube, data were extracted along a curved slit that matches the trajectory of the gas cloud and from a fit to the gas emission lines in the spectra, the velocity of the cloud was deduced for each position along the slit. The resulting plot shows at which velocity (x axis) the gas is moving depending on its position on the orbit (y axis) and color-coded for the epoch of observation (2008: red, 2011: blue, 2012: green). Apart from the cloud itself, a slow moving tail with velocities < 1000 km/s is seen. While the observations clearly show that the gas cloud is being disrupted, up to now the evolution of the cloud can be fully explained with a simple test particle simulation without any hydrodynamical effects.

In the course of this year, more observations of the cloud are planned, of course, and not only in the infrared but campaigns have been started by many groups to observe this accretion event in the whole electromagnetic spectrum. A wiki page has been set up to collect all information on "G2".

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This composite image shows the positions of the gas cloud in 2002, 2007, and 2011 marked in colour. The cross indicates the position of the black hole in the galactic centre.
Image: MPE

Galactic Black Hole disrupts Gas Cloud

Over the next few years, astronomers will be able to observe first-hand how the super massive black hole at the centre of our Milky Way is being fed: an international team of astronomers led by the Max Planck Institute for Extraterrestrial Physics has found a gas cloud that is falling towards the black hole in the galactic centre. While some distortion due to the huge gravitational pull of the black hole can already be seen, the gas cloud will be completely disrupted and ultimately swallowed by the black hole, resulting in largely increased X-ray emission. The observations and analysis are described in a Nature paper, published online on 14 December 2011.



For more information see
    MPE Press Release.
(Dec 14, 2011)

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This illustration shows an Ultra-Luminous InfraRed Galaxy (ULIRG) that exhibits massive outflows of molecular gas.
Image: MPE

Caught in the act: Herschel detects gigantic storms sweeping entire galaxies clean

With observations from the PACS instrument on board the ESA Herschel space observatory, an international team of scientists led by the Max Planck Institute for Extraterrestrial Physics have found gigantic storms of molecular gas gusting in the centres of many galaxies. Some of these massive outflows reach velocities of more than 1000 kilometres per second, i.e. thousands of times faster than in terrestrial hurricanes. The observations show that the more active galaxies contain stronger winds, which can blow away the entire gas reservoir in a galaxy, thereby inhibiting both further star formation and the growth of the central black hole. This finding is the first conclusive evidence for the importance of galactic winds in the evolution of galaxies.



For more information see
    MPE Press Release.
(May 09, 2011)

 
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