arXiv subjects

Eric M. Huff

Publications and source records attributed to Eric M. Huff.

21 records · Page 2Linked to original sources

arXiv2011

Magnificent Magnification: Exploiting the Other Half of the Lensing Signal

We describe a new method for measuring galaxy magnification due to weak gravitational lensing. Our method makes use of a tight scaling relation between galaxy properties that are modified by gravitational lensing, such as apparent size, and other properties that are not, such as surface brightness. In particular, we use a version of the well-known fundamental plane relation for early type galaxies. This modified "photometric fundamental plane" replaces velocity dispersions with photometric galaxy properties, thus obviating the need for spectroscopic data. We present the first detection of magnification using this method by applying it to photometric catalogs from the Sloan Digital Sky Survey. This analysis shows that the derived magnification signal is comparable to that available from conventional methods using gravitational shear. We suppress the dominant sources of systematic error and discuss modest improvements that may allow this method to equal or even surpass the signal-to-noise achievable with shear. Moreover, some of the dominant sources of systematic error are substantially different from those of shear-based techniques. Thus, combining the two techniques addresses the major weaknesses of each and provides a substantial improvement over either method used in isolation. With this new technique, magnification becomes a necessary measurement tool for the coming era of large ground-based surveys intending to measure gravitational lensing.

astro-ph.CO↗

arXiv2008

The Spectral Energy Distributions of Red 2MASS AGN

We present infrared (IR) to X-ray spectral energy distributions (SEDs) for 44 red AGN selected from the 2MASS survey on the basis of their red J-K$_S$ color (>2 mag) and later observed by Chandra. In comparison with optically-, radio-, and X-ray selected AGN, their median SEDs are red in the optical and near-IR with little/no blue bump. It thus seems that near-IR color selection isolates the reddest subset of AGN that can be classified optically. The shape of the SEDs is generally consistent with modest absorption by gas (in the X-ray) and dust (in the optical-IR). The levels of obscuration, estimated from X-rays, far-IR and our detailed optical/near-IR color modeling are all consistent implying N_H < few*10^{22} cm^{-2}. We present SED models that show how the AGN optical/near-IR colors change due to differing amounts of reddening, AGN to host galaxy ratio, redshift and scattered light emission and apply them to the sources in the sample. We find that the 2MASS AGN optical color, B-R, and to a lesser extent the near-IR color, J-K$_S$, are strongly affected by reddening, host galaxy emission, redshift, and in few, highly polarized objects, also by scattered AGN light. The obscuration/inclination of the AGN allows us to see weaker emission components which are generally swamped by the AGN.

astro-ph↗

arXiv2006

Star Formation in Space and Time: The Orion Nebula Cluster

We examine the pattern of star birth in the Orion Nebula Cluster (ONC), with the goal of discerning the cluster's formation mechanism. Outside of the Trapezium, the distribution of stellar masses is remarkably uniform, and is not accurately described by the field-star initial mass function. The deconvolved, three-dimensional density of cluster members peaks at the Trapezium stars, which are truly anomalous in mass. Using theoretical pre-main-sequence tracks, we confirm the earlier finding that star formation has accelerated over the past 10 Myr. We further show that the rate of acceleration has been the same for all masses. Thus, there is no correlation between stellar age and mass, contrary to previous claims. Finally, the acceleration has been spatially uniform throughout the cluster. Our reconstruction of the parent molecular cloud spawning the cluster shows that it had a mass of 6700 solar masses prior to its destruction by the Trapezium. If the cloud was supported against self-gravity by mildly dissipative turbulence, then it contracted in a quasi-static, but accelerating manner. We demonstrate this contraction theoretically through a simple energy argument. The mean turbulent speed increased to its recent value, which is reflected in the present-day stellar velocity dispersion. The current ONC will be gravitationally unbound once cloud destruction is complete, and is destined to become a dispersing OB association. We hypothesize that similarly crowded groups seen at the centers of distant OB associations are also unbound, and do not give rise to the Galactic population of open clusters. Finally, accelerating star formation implies that most clumps within giant molecular complexes should have relatively low formation activity. Sensitive infrared surveys could confirm this hypothesis.

astro-ph↗