Recent Results of the MPE Infrared/Submillimeter Group
ALMA Reveals the Rapid Evolutionary Lifecycle of Star-Forming Regions in Galaxies
Determining the physical processes controlling star formation in molecular clouds remains one of the main unsolved problems in astrophysics. New high-resolution observations of molecular clouds from ALMA and of the emission of young stars from the MPG/ESO 2.2 meter telescope for the nearby spiral galaxy NGC300 highlight the weak correlation of young stars and their parent clouds. This implies that the close correlation between molecular gas and star formation rate observed for whole galaxies and down to kpc scales – known as the Kennicutt-Schmidt or star formation relation – results from averaging over many star-forming relations. With a novel statistical model, we have shown that the observed decorrelation of young stars and molecular clouds holds valuable information on the time evolution of star-forming regions. For NGC300, we find that molecular clouds are short-lived (10 Myr or 1 dynamical timescale) and that a short period of active star formation (1.5 Myr) during which 2 to 3% of the cloud's mass is turned into stars releases sufficient stellar radiation and winds to disperse the parent molecular cloud. Star formation in molecular clouds proceeds very rapidly, yet highly inefficiently. This also explains the slow consumption of the galactic molecular gas reservoir by star formation of 1 Gyr in nearby galaxies because molecular gas has to evolve through many such cycles before it is fully turned into stars. We are now applying this analysis to a large number of galaxies in the nearby universe studied by the PHANGS collaboration and to first high-resolution observations of galaxies at high redshift during the peak of cosmic star formation.
- MPE press release
- Research paper: Kruijssen, Schruba et al., Nature Vol. 569, Issue 7757, p. 519–522
A Spatially Resolved Quasar Broad-Line Region
Knowing the structure, size, and dynamics of the broad-line regions (BLRs) near accreting supermassive black holes would allow scientists to constrain the inward and outward transport mechanisms and to infer the mass of the black hole. So far, however, directly measuring BLR properties was impossible because of the small physical size of the BLR, on the order of hundreds of light-days (corresponding to an angular size < 1 milliarcseconds). With GRAVITY, we have now, for the first time, spatially resolved (10 microarcseconds or ~ 0.03 parsec for a distance of 550 megaparsecs) a velocity gradient across the BLR of the quasar 3C 273. The gradient reveals rotation perpendicular to the jet, and is consistent with line emission from a thick disc of gravitationally bound material around a black hole of 3x108 M☉. We infer a disc radius of 150 light-days, compared to 100 to 400 light-days found previously with reverberation mapping (RM). Thus, GRAVITY provides both a confirmation of RM (at least for this one object) as the main previous method to determine black hole masses in quasars and a new and highly accurate, independent method to measure such masses. In an approved VLTI Large Program, we will extend this study to a (small) sample of local AGN, and we are exploring options to expand it to larger samples and higher redshifts with potential upgrades of GRAVITY.
More information: MPE News
Measurement of Gravitational Redshift in the Galactic Center
Sagittarius A* (Sgr A*), the massive black hole in the center of our galaxy, is the closest of its kind and the largest in the sky. It is surrounded by a cluster of high-velocity stars, called the S-stars, whose trajectories are governed by the gravitational field of the black hole. We used the Very Large Telescope (VLT) instruments GRAVITY and SINFONI to follow the short (16-year) orbit star S2/S-02 during its recent pericenter passage in May 2018, and collected astrometric and spectroscopic data, respectively. For the first time, these joint data allowed for a robust detection of the combined gravitational redshift and transverse Doppler effect on S2/S-02.
Gravitational redshift is one of the three classic tests of general relativity. Einstein's theory foresees that due to gravitational time dilation, a light beam is stretched to longer wavelengths by a gravitational field. The change in the wavelength of light from S2/S-02 is inconsistent with Newtonian predictions and in excellent agreement with Einstein’s general theory of relativity. On a technological level, the success of this measurement with GRAVITY/VLT opens the door to an entirely new type of laboratory to probe and test the theory: the Galactic Center.
More information: GRAVITY Collaboration, 2018A&A...615L..15G
Outflow Demographics and Physical Properties at z ~ 1–3
Exploiting our full KMOS3D and SINS/zC-SINF surveys of near-IR IFU spectroscopy of z ~ 1–3 galaxies, we obtained the most complete census to date of galactic-scale ionized gas outflows at the peak epoch of cosmic star formation and AGN activity. The sample of ~ 600 primarily mass-selected galaxies spans wide ranges in stellar mass and star formation rate; the selection by mass, rather than by properties biased toward star formation (SF) or AGN activity, makes it ideally suited for a population-averaged characterization of winds as relevant to galaxy evolution. Compared to slit spectra, the IFU data greatly facilitate the separation between the broad outflow component in Hα+[NII]+[SII] and the narrower component from SF. Our studies show how outflows driven by SF and AGN are spatially, spectrally, and demographically distinct. SF-driven winds, launched near bright star-forming clumps across disks, have typical speeds of ~ 450 km/s below the hosts’ escape velocity except at log(M⁎/M☉) < 10.3; the prevalence of these winds depends on SF properties, not mass. AGN-driven winds originate from the nuclear regions, are ubiquitous in log(M⁎/M☉) > 10.7 galaxies hosting a massive bulge but rare at lower masses, irrespective of SF activity; with velocities of ~ 1,500 km/s, they can escape the galaxies. For the first time, the high S/N spectra constrain the density in high-z SF-driven winds from the broad [SII] doublet ratio, yielding ne ~ 400 cm-3; for AGN-driven winds, a higher ne ~ 1,000 cm-3 is inferred. These densities are a factor of several higher than previously assumed values, and lead to correspondingly more modest mass outflow rates ~ 0.1–0.4 x SFRs in warm ionized gas. The tension with theoretical work, requiring mass outflow rates ≳ SFRs to reproduce the observed relationships between galaxy mass and metallicity as well as galaxy mass and halo mass at log(M⁎/M☉) < 10.7, could be alleviated if substantial mass, momentum, and energy were ejected in hotter and/or colder phases than the ~ 104 K ionized gas probed by our data. The fast, high-duty-cycle AGN-driven winds at high masses carry significant energy (~ 1% that of the AGN), which may contribute to heat halo gas and help prevent further gas infall. Our results are consistent with recent EAGLE and Illustris/TNG numerical simulations, which suggest that such a mechanism, acting also at the modest luminosities and Eddington ratios of the majority of the KMOS3D and SINS/zC-SINF AGN, may be more effective at widespread and long-term quenching than ejective "QSO mode" feedback in rare, high-luminosity, high-Eddington-ratio AGN.
More information: Research paper: Förster Schreiber, Übler, Davies et al. 2019, ApJ, 875, 21
Scaling Relations for Molecular Gas in Galaxies over Cosmic Time
We have developed new statistically robust scaling relations between galaxy-integrated molecular gas masses, stellar masses, and star formation rates (SFRs) relative to that on the main sequence (δMS). Combining data from our PHIBSS and xCOLDGASS surveys with information available in literature, we use three independent methods to determine molecular gas masses: 1) CO line fluxes, 2) Herschel far-infrared dust SEDs, and 3) ~ 1 mm dust photometry, in a large sample of 1,444 star-forming galaxies and stacks between z = 0 and 4. The sample spans stellar masses from log(M⁎/M☉) = 9.0–11.8, and SFRs relative to that on the MS, from 10-1.3 to 102.2. The most important result is that all data sets follow the same scaling trends, once we account for uncertainties and apply consistent methodologies. The molecular gas depletion time tdepl, defined molecular gas mass/star formation rate, scales as (1+z)-0.6 x (δMS)-0.44, and is only weakly dependent on stellar mass. The ratio of molecular to stellar mass μgas depends on (1+z)2.5 x (δMS)0.52 x (M⁎)-0.36, and tracks the evolution of the specific SFR.
- Research paper: Tacconi et al. 2018 ApJ 853, 179
- Research paper: Genzel et al. 2015 ApJ 800, 20
- Research paper: Tacconi et al. 2013 ApJ 768, 74
Strongly Baryon-dominated Disk Galaxies at the Peak Epoch of Galaxy Formation
New observations of rotating galaxies at z ~ 2, the peak epoch of galaxy formation, show that these massive star-forming galaxies are strongly dominated by baryonic mass, with dark matter playing a much smaller role in comparable regions of their outer disks than in typical present-day spiral galaxies. This result was obtained from observations of unprecedented sensitivity with the SINFONI and KMOS near-IR integral field spectrometers, mapping the 2D kinematics of ionized gas through the Hα line emission of six galaxies out to two to three times their half-light radius. On these scales, dark matter starts to dominate the total mass budget in z ~ 0 late-type galaxies, causing their rotation curves to stay mostly flat or slightly increase with radius. In contrast, the six individual massive z ~ 2 galaxies in our study exhibit declining rotation curves, which can be explained by the combination of two factors: baryons dominate more strongly than dark matter on galactic scales, and the elevated gas turbulence characteristic of z ~ 2 disks provides a significant amount of the dynamical support, thereby leading to a decrease in the rotation velocity. Such a falloff with radius is further seen in the average outer rotation curve derived through a novel stacking technique of ~ 100 typical massive z ~ 1–2.5 disk galaxies observed with KMOS and SINFONI, suggesting that it is a common feature among the star-forming population in these epochs. Two additional studies of the resolved inner disk kinematics (out to 1–1.5 half-light radius or the velocity turnover radius) of 240 star-forming disks support the results based on the outer rotation curves. Detailed dynamical modeling shows that while the stars and gas account on average for ~ 56% of the total enclosed mass at z ~ 1–2.5, the baryon fraction reaches ~ 90% at the higher redshifts, and is largest in disks with highest central baryonic mass surface density. The evolution of the zero point of the stellar and baryonic Tully-Fisher relationships based on the same data is further compatible with the increase in gas and baryon mass fractions with redshift, with a lesser role of dark matter in the central disk regions. The low-galactic-scale dark matter fractions found in massive high-redshift galaxies in these studies are comparable to those of present-day massive early-type galaxies, their likely descendants. The high gas fractions in z ~ 2 star-forming galaxies could help to dissipate angular momentum, efficiently driving gas inward and leading to the strong dominance of baryons early on.
- MPE News
- Research paper: Genzel et al. 2017, Nature, 543, 397
- Research paper: Lang et al. 2017, ApJ, 840, 92
- Research paper: Übler et al. 2017, ApJ, 842, 121
- Research paper: Wuyts et al. 2016, ApJ, 831, 149
KMOS3D Survey of Spatially Resolved Gas Kinematics, Star Formation, and ISM Properties Sheds New Light on the Physics of Galaxy Evolution
Our comprehensive and highly successful multi-year KMOS3D survey takes advantage of the efficient multiplexing of the new near-IR 24-IFU KMOS instrument at the Very Large Telescope to spatially resolve the ionized gas kinematics, star formation, outflows, excitation, and metallicities of a large and homogeneous sample of z ~ 0.7−2.7 mass-selected galaxies. KMOS3D is a 75-night Guaranteed Time Program started in November 2013 and led by the MPE Infrared/Submillimeter Group and MPE/OPINAS and USM. After 2.5 years and 52 nights of productive observing campaigns, the sample has now reached 564 galaxies, with an overall Hα detection fraction of 80% (and as high as 90% for main-sequence star-forming galaxies). The survey was carried out in well-studied extragalactic fields, benefitting from extensive multiwavelength data that include the far-IR Herschel PEP survey and high-resolution near-IR/optical grism and imaging data from the 3D-HST/CANDELS HST Treasury programs. KMOS3D is designed to provide an unbiased census from deep integrations (~ 5 to 25 hours) of the Hα+[NII]+[SII] line emission resolved on seeing-limited scales of 4 to 5 kiloparsecs, over a wide range of galaxy parameters and five billion years of cosmic time. The strategy is uniquely enabling faint-line emission mapping in individual objects and pushing near-IR IFU studies into new regimes, such as lower-mass star-forming galaxies and high-mass submain-sequence galaxies in the process of quenching. The ighlights of our results are shown in the figure below. They robustly confirm the earlier findings from our SINS/zC-SINF near-IR IFU survey with SINFONI on the majority of disks among high-z star-forming galaxies and their elevated gas turbulence compared to present-day spirals, and on the ubiquity and origin of powerful AGN- and star-formation-driven gas outflows. They also provide new constraints on the angular momenta, baryonic mass fractions, outer disk structure, the relation between mass, metallicity, and star formation, and gas phase O/H abundance gradients. Furthermore, our results shed new light on dense core formation and star formation quenching in high-mass galaxies.
- Research paper: Wisnioski et al. 2015, ApJ, 799, 209
- Research paper: Burkert et al. 2016, ApJ, 826, 214
- Research paper: Wuyts et al. 2016, ApJ, 831, 149
- Research paper: Wuyts et al. 2016, ApJ, 827, 74
ALMA Reveals Planetary Construction Sites
By using the Atacama Large Millimeter/submillimeter Array (ALMA), we have discovered the clearest indications yet that planets with masses several times that of Jupiter have recently formed in the discs around young stars. New images of transitional discs show that there are significant amounts of gas within the dust gaps, and that the gas also possessed a gap, which was up to three times smaller than that of dust. This can only be explained by a scenario in which newly formed massive planets clear the gas as they travel around their orbits, but trap the dust particles further out. The data rule out other scenarios for the observed set of discs.
More information: ESO Press Release
Evidence for Widespread AGN-driven Outflows in the Most Massive z ~ 1–2 Star-forming Galaxies
Very deep laser guide star-assisted adaptive-optics observations allowed us to detect ubiquitous powerful nuclear outflows in massive (1011 M☉) 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 [NII] and [SII] line emission, with typical velocity FWHM ∼ 1,500 km s-1, high [NII]/Hα ratio ~ 0.6, and intrinsic extent of 2 to 3 kiloparsecs. 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, that act across the peak of cosmic galaxy formation.
- Research paper: Förster Schreiber et al. 2014, ApJ 787, 38
- Research paper: Genzel et al. 2014, ApJ 796, 7
Molecular Gas, Extinction, Star Formation, and Kinematics in the z = 1.5 Star-forming Galaxy EGS130111661
As a follow-up to the high-redshift molecular gas survey PHIBBS (Tacconi et al. 2013; see news item below), we carried out a detailed analysis 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 Hα line in this galaxy, at matched spatial resolutions of 0.75 arcseconds. The galaxy was scanned perpendicularly to the slit with LUCI to obtain spectra that are spatially resolved both along and perpendicular to the slit. Additionally, we used Hubble Space Telescope (HST) V-, I-, J-, and H-band maps. Together, these data allow us to derive the stellar surface density and star formation rate, molecular gas surface density, optical extinction, and gas kinematics.
More information: Research paper: Genzel et al. 2013, ApJ, 778, 68
New Observations on the Galactic Center Gas Cloud "G2"
September 12, 2012
New observations on the gas cloud "G2" falling toward the Galactic Center confirm its highly elliptical orbit, but with updated orbital parameters. As new data show, the cloud is now expected to come even closer – the updated pericenter distance is 2200 Schwarzschild radii – to the supermassive 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.
In the course of this year, we have planned more observations of the cloud, of course, and not only in the infrared area. Many groups have started campaigns to observe this accretion event in the whole electromagnetic spectrum. A wiki page has been set up to collect all information on "G2."
More information: Research paper: Gillessen et al. 2013, ApJ, 763, 78
Galactic Black Hole Disrupts Gas Cloud
December 14, 2011
Over the next few years, astronomers will be able to observe first-hand how the supermassive black hole at the center 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 toward the black hole in the Galactic Center. 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 December 14, 2011.
More information: MPE Press Release
Caught in the act: Herschel Detects Gigantic Storms Sweeping Entire Galaxies Clean
May 9, 2011
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 has found gigantic storms of molecular gas gusting in the centers of many galaxies. Some of these massive outflows reach velocities of more than 1,000 km/s, i.e., they are thousands of times faster than the ones 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.
More information: MPE Press Release