arXiv subjects

Douglas P. Finkbeiner

Publications and source records attributed to Douglas P. Finkbeiner.

At least 73 records · Page 4Linked to original sources

arXiv2012

Is the 130 GeV Line Real? A Search for Systematics in the Fermi-LAT Data

Our recent claims of a Galactic center feature in Fermi-LAT data at approximately 130 GeV have prompted an avalanche of papers proposing explanations ranging from dark matter annihilation to exotic pulsar winds. Because of the importance of such interpretations for physics and astrophysics, a discovery will require not only additional data, but a thorough investigation of possible LAT systematics. While we do not have access to the details of each event reconstruction, we do have information about each event from the public event lists and spacecraft parameter files. These data allow us to search for suspicious trends that could indicate a spurious signal. We consider several hypotheses that might make an instrumental artifact more apparent at the Galactic center, and find them implausible. We also search for an instrumental signature in the Earth limb photons, which provide a smooth reference spectrum for null tests. We find no significant 130 GeV feature in the Earth limb sample. However, we do find a marginally significant 130 GeV feature in Earth limb photons with a limited range of detector incidence angles. This raises concerns about the 130 GeV Galactic center feature, even though we can think of no plausible model of instrumental behavior that connects the two. A modest amount of additional limb data would tell us if the limb feature is a statistical fluke. If the limb feature persists, it would raise doubts about the Pass 7 processing of E > 100 GeV events. At present we find no instrumental systematics that could plausibly explain the excess Galactic center emission at 130 GeV.

astro-ph.HE↗

arXiv2012

Double Gamma-ray Lines from Unassociated Fermi-LAT Sources

Gamma ray emission from dark matter subhalos in the Milky Way has long been sought as a sign of dark matter particle annihilation. So far, searches for gamma-ray continuum from subhalos have been unsuccessful, and line searches are difficult without prior knowledge of the line energies. Guided by recent claims of line emission at 111 GeV and 129 GeV in the Galactic center, we examine the co-added gamma-ray spectrum of unassociated point sources in the Second Fermi-LAT catalog (2FGL) using 3.9 years of LAT data. Using the SOURCE event class, we find evidence for lines at 111 GeV and 129 GeV with a local significance of 3.3 sigma based on a conservative estimate of the background at E>135 GeV. Other 2FGL sources analyzed in the same way do not show line emission at 111 GeV and 129 GeV. The line-emitting sources are mostly within 30 degrees of the Galactic plane, although this anisotropy may be a selection effect. If the double-line emission from these objects is confirmed with future data, it will provide compelling support for the hypothesis that the Galactic center line signal is indeed from dark matter annihilation.

astro-ph.HE↗

arXiv2012

Strong Evidence for Gamma-ray Line Emission from the Inner Galaxy

Using 3.7 years of \Fermi-LAT data, we examine the diffuse 80-200 GeV emission in the inner Galaxy and find a resolved gamma-ray feature at $\sim 110-140$ GeV. We model the spatial distribution of this emission with a $\sim3\degree$ FWHM Gaussian, finding a best fit position $1.5\degree$ West of the Galactic Center. Even better fits are obtained for off-center Einasto and power-law profiles, which are preferred over the null (no line) hypothesis by $6.5σ$ ($5.0σ/5.4σ$ after trials factor correction for one/two line case) assuming an NFW density profile centered at $(\ell, b)=(-1.5\degree,0\degree)$ with a power index $α=1.2$ . The energy spectrum of this structure is consistent with a single spectral line (at energy $127.0\pm 2.0$ GeV with $χ^2=4.48$ for 4 d.o.f.). A pair of lines at $110.8\pm 4.4$ GeV and $128.8\pm 2.7$ GeV provides a marginally better fit (with $χ^2=1.25$ for 2 d.o.f.). The total luminosity of the structure is $(3.2\pm0.6)\times 10^{35}$ erg/s, or $(1.7\pm0.4)\times 10^{36}$ photons/sec. The energies in the two-line case are compatible with a $127.3 \pm 2.7$ GeV WIMP annihilating through $γγ$ and $γZ$ (with $χ^2=1.67$ for 3 d.o.f.). We describe a possible change to the \Fermi\ scan strategy that would accumulate S/N on spectral lines in the Galactic center 4 times as fast as the current survey strategy.

astro-ph.HE↗

arXiv2012

Evidence for Gamma-ray Jets in the Milky Way

Although accretion onto supermassive black holes in other galaxies is seen to produce powerful jets in X-ray and radio, no convincing detection has ever been made of a kpc-scale jet in the Milky Way. The recently discovered pair of 10 kpc tall gamma-ray bubbles in our Galaxy may be a sign of earlier jet activity from the central black hole. In this paper, we identify a gamma-ray cocoon feature in the southern bubble, a jet-like feature along the cocoon's axis of symmetry, and another directly opposite the Galactic center in the north. Both the cocoon and jet-like feature have a hard spectrum with spectral index ~ -2 from 1 to 100 GeV, with a cocoon luminosity of (5.5 +/- 0.45) x 10^35 erg/s and luminosity of the jet-like feature of (1.8 +/- 0.35) x 10^35 erg/s at 1 to 100 GeV. If confirmed, these jets are the first resolved gamma-ray jets ever seen.

astro-ph.HE↗

arXiv2012

The Metallicity of the Monoceros Stream

We present low-resolution MMT Hectospec spectroscopy of 594 candidate Monoceros stream member stars. Based on strong color-magnitude diagram overdensities, we targeted three fields within the stream's footprint, with 178 deg < l < 203 deg and -25 deg < b < 25 deg. By comparing the measured iron abundances with those expected from smooth Galactic components alone, we measure, for the first time, the spectroscopic metallicity distribution function for Monoceros. We find the stream to be chemically distinct from both the thick disk and halo, with [Fe/H] = -1, and do not detect a trend in the stream's metallicity with Galactic longitude. Passing from b = +25 deg to b = -25 deg the median Monoceros metallicity trends upward by 0.1 dex, though uncertainties in modeling sample contamination by the disk and halo make this a marginal detection. In each field, we find Monoceros to have an intrinsic [Fe/H] dispersion of 0.10-0.22 dex. From the CaII K line, we measure [Ca/Fe] for a subsample of metal poor program stars with -1.1 < [Fe/H] < -0.5. In two of three fields, we find calcium deficiencies qualitatively similar to previously reported [Ti/Fe] underabundances in Monoceros and the Sagittarius tidal stream. Further, using 90 spectra of thick disk stars in the Monoceros pointings with b ~ +/-25 deg, we detect a 0.22 dex north/south metallicity asymmetry coincident with known stellar density asymmetry at R_GC ~ 12 kpc and |Z| ~ 1.7 kpc. Our median Monoceros [Fe/H] = -1.0 and its relatively low dispersion naturally fit the expectation for an appropriately luminous M_V ~ -13 dwarf galaxy progenitor.

astro-ph.GA↗

arXiv2012

The DEEP2 Galaxy Redshift Survey: Design, Observations, Data Reduction, and Redshifts

We describe the design and data sample from the DEEP2 Galaxy Redshift Survey, the densest and largest precision-redshift survey of galaxies at z ~ 1 completed to date. The survey has conducted a comprehensive census of massive galaxies, their properties, environments, and large-scale structure down to absolute magnitude M_B = -20 at z ~ 1 via ~90 nights of observation on the DEIMOS spectrograph at Keck Observatory. DEEP2 covers an area of 2.8 deg^2 divided into four separate fields, observed to a limiting apparent magnitude of R_AB=24.1. Objects with z < 0.7 are rejected based on BRI photometry in three of the four DEEP2 fields, allowing galaxies with z > 0.7 to be targeted ~2.5 times more efficiently than in a purely magnitude-limited sample. Approximately sixty percent of eligible targets are chosen for spectroscopy, yielding nearly 53,000 spectra and more than 38,000 reliable redshift measurements. Most of the targets which fail to yield secure redshifts are blue objects that lie beyond z ~ 1.45. The DEIMOS 1200-line/mm grating used for the survey delivers high spectral resolution (R~6000), accurate and secure redshifts, and unique internal kinematic information. Extensive ancillary data are available in the DEEP2 fields, particularly in the Extended Groth Strip, which has evolved into one of the richest multiwavelength regions on the sky. DEEP2 surpasses other deep precision-redshift surveys at z ~ 1 in terms of galaxy numbers, redshift accuracy, sample number density, and amount of spectral information. We also provide an overview of the scientific highlights of the DEEP2 survey thus far. This paper is intended as a handbook for users of the DEEP2 Data Release 4, which includes all DEEP2 spectra and redshifts, as well as for the publicly-available DEEP2 DEIMOS data reduction pipelines. [Abridged]

astro-ph.CO↗

arXiv2011

Searching for Dark Matter in the CMB: A Compact Parameterization of Energy Injection from New Physics

High-precision measurements of the temperature and polarization anisotropies of the cosmic microwave background radiation have been previously employed to set robust constraints on dark matter annihilation during recombination. In this work we improve and generalize these constraints to apply to energy deposition during the recombination era with arbitrary redshift dependence. Our approach also provides more rigorous and model-independent bounds on dark matter annihilation and decay scenarios. We employ principal component analysis to identify a basis of weighting functions for the energy deposition. The coefficients of these weighting functions parameterize any energy deposition model and can be constrained directly by experiment. For generic energy deposition histories that are currently allowed by WMAP7 data, up to 3 principal component coefficients are measurable by Planck and up to 5 coefficients are measurable by an ideal cosmic variance limited experiment. For WIMP dark matter, our analysis demonstrates that the effect on the CMB is described well by a single (normalization) parameter and a "universal" redshift dependence for the energy deposition history. We give WMAP 7 constraints on both generic energy deposition histories and the universal WIMP case.

astro-ph.CO↗

arXiv2011

Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD

We present measurements of dust reddening using the colors of stars with spectra in the Sloan Digital Sky Survey. We measure reddening as the difference between the measured and predicted colors of a star, as derived from stellar parameters from the SEGUE Stellar Parameter Pipeline (Lee et al. 2008a). We achieve uncertainties of 56, 34, 25, and 29 mmag in the colors u-g, g-r, r-i, and i-z, per star, though the uncertainty varies depending on the stellar type and the magnitude of the star. The spectrum-based reddening measurements confirm our earlier "blue tip" reddening measurements (Schlafly et al. 2010, S10), finding reddening coefficients different by -3%, 1%, 1%, and 2% in u-g, g-r, r-i, and i-z from those found by the blue tip method, after removing a 4% normalization difference. These results prefer an R_V=3.1 Fitzpatrick (1999) reddening law to O'Donnell (1994) or Cardelli et al. (1989) reddening laws. We provide a table of conversion coefficients from the Schlegel et al. (1998) maps of E(B-V) to extinction in 88 bandpasses for 4 values of R_V, using this reddening law and the 14% recalibration of SFD first reported by S10 and confirmed in this work.

astro-ph.GA↗

arXiv2011

Magnetic Inelastic Dark Matter: Directional Signals Without a Directional Detector

The magnetic inelastic dark matter (MiDM) model, in which dark matter inelastically scatters off nuclei through a magnetic dipole interaction, has previously been shown to reconcile the DAMA/LIBRA annual modulation signal with null results from other experiments. In this work, we explore the unique directional detection signature of MiDM. After the dark matter scatters into its excited state, it decays with a lifetime of order 1 microsecond and emits a photon with energy ~100 keV. Both the nuclear recoil and the corresponding emitted photon can be detected by studying delayed coincidence events. The recoil track and velocity of the excited state can be reconstructed from the nuclear interaction vertex and the photon decay vertex. The angular distribution of the WIMP recoil tracks is sharply peaked and modulates daily. It is therefore possible to observe the directional modulation of WIMP-nucleon scattering without a large-volume gaseous directional detection experiment. Furthermore, current experiments such as XENON100 can immediately measure this directional modulation and constrain the MiDM parameter space with an exposure of a few thousand kg day.

astro-ph.CO↗

arXiv2011

Consistent Scenarios for Cosmic-Ray Excesses from Sommerfeld-Enhanced Dark Matter Annihilation

Anomalies in direct and indirect detection have motivated models of dark matter consisting of a multiplet of nearly-degenerate states, coupled by a new GeV-scale interaction. We perform a careful analysis of the thermal freezeout of dark matter annihilation in such a scenario. We compute the range of "boost factors" arising from Sommerfeld enhancement in the local halo for models which produce the correct relic density, and show the effect of including constraints on the saturated enhancement from the cosmic microwave background (CMB). We find that boost factors from Sommerfeld enhancement of up to ~800 are possible in the local halo. When the CMB bounds on the saturated enhancement are applied, the maximal boost factor is reduced to ~400 for 1-2 TeV dark matter and sub-GeV force carriers, but remains large enough to explain the observed Fermi and PAMELA electronic signals. We describe regions in the DM mass-boost factor plane where the cosmic ray data is well fit for a range of final states, and show that Sommerfeld enhancement alone is enough to provide the large annihilation cross sections required to fit the data, although for light mediator masses (less than ~200 MeV) there is tension with the CMB constraints in the absence of astrophysical boost factors from substructure. Additionally, we consider the circumstances under which WIMPonium formation is relevant and find for heavy WIMPs (greater than ~2 TeV) and soft-spectrum annihilation channels it can be an important consideration; we find regions with dark matter mass greater than 2.8 TeV that are consistent with the CMB bounds and have ~600-700 present-day boost factors.

hep-ph↗

arXiv2010

Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?

Data from the Fermi-LAT reveal two large gamma-ray bubbles, extending 50 degrees above and below the Galactic center, with a width of about 40 degrees in longitude. The gamma-ray emission associated with these bubbles has a significantly harder spectrum (dN/dE ~ E^-2) than the IC emission from electrons in the Galactic disk, or the gamma-rays produced by decay of pions from proton-ISM collisions. There is no significant spatial variation in the spectrum or gamma-ray intensity within the bubbles, or between the north and south bubbles. The bubbles are spatially correlated with the hard-spectrum microwave excess known as the WMAP haze; the edges of the bubbles also line up with features in the ROSAT X-ray maps at 1.5-2 keV. We argue that these Galactic gamma-ray bubbles were most likely created by some large episode of energy injection in the Galactic center, such as past accretion events onto the central massive black hole, or a nuclear starburst in the last ~10 Myr. Dark matter annihilation/decay seems unlikely to generate all the features of the bubbles and the associated signals in WMAP and ROSAT; the bubbles must be understood in order to use measurements of the diffuse gamma-ray emission in the inner Galaxy as a probe of dark matter physics. Study of the origin and evolution of the bubbles also has the potential to improve our understanding of recent energetic events in the inner Galaxy and the high-latitude cosmic ray population.

astro-ph.HE↗

arXiv2010

The Blue Tip of the Stellar Locus: Measuring Reddening with the SDSS

We present measurements of reddening due to dust using the colors of stars in the Sloan Digital Sky Survey (SDSS). We measure the color of main sequence turn-off stars by finding the "blue tip" of the stellar locus: the prominent blue edge in the distribution of stellar colors. The method is sensitive to color changes of order 18, 12, 7, and 8 mmag of reddening in the colors u-g, g-r, r-i, and i-z, respectively, in regions measuring 90' by 14'. We present maps of the blue tip colors in each of these bands over the entire SDSS footprint, including the new dusty southern Galactic cap data provided by the SDSS-III. The results disfavor the best fit O'Donnell (1994) and Cardelli et al. (1989) reddening laws, but are well described by a Fitzpatrick (1999) reddening law with R_V = 3.1. The SFD dust map is found to trace the dust well, but overestimates reddening by factors of 1.4, 1.0, 1.2, and 1.4 in u-g, g-r, r-i, and i-z, largely due to the adopted reddening law. In select dusty regions of the sky, we find evidence for problems in the SFD temperature correction. A dust map normalization difference of 15% between the Galactic north and south sky may be due to these dust temperature errors.

astro-ph.GA↗

arXiv2010

Inelastic Dark Matter and DAMA/LIBRA: An Experimentum Crucis

The DAMA/LIBRA collaboration has detected an annual modulation of the recoil rate in NaI crystals with the phase expected for WIMP scattering events. This signal is dramatically inconsistent with upper limits from other experiments for elastically scattering weak-scale WIMPs. However, the results are compatible for the case of inelastic dark matter (iDM). The iDM theory, as implemented by Tucker-Smith and Weiner, constrains the WIMP to a tight contour in sigma_n-delta space, where delta is the mass difference between the ground state and excited WIMPs. An urgent priority in direct detection is to test this scenario. The crucial test of the iDM explanation of DAMA -- an "experimentum crucis" -- is an experiment with directional sensitivity, which can measure the daily modulation in direction. Because the contrast can be 100%, it is a sharper test than the much smaller annual modulation in the rate. We estimate the significance of such an experiment as a function of the WIMP mass, cross section, background rate, and other parameters. The proposed experiment severely constrains the DAMA/iDM scenario even with modest exposure (~1000 kg day) on gaseous xenon.

astro-ph.CO↗

arXiv2010

The Electron Injection Spectrum Determined by Anomalous Excesses in Cosmic Ray, Gamma Ray, and Microwave Signals

Recent cosmic ray, gamma ray, and microwave signals observed by Fermi, PAMELA, and WMAP indicate an unexpected primary source of e+e- at 10-1000 GeV. We fit these data to "standard backgrounds" plus a new source, assumed to be a separable function of position and energy. For the spatial part, we consider three cases: annihilating dark matter, decaying dark matter, and pulsars. In each case, we use GALPROP to inject energy in log-spaced energy bins and compute the expected cosmic-ray and photon signals for each bin. We then fit a linear combination of energy bins, plus backgrounds, to the data. We use a non-parametric fit, with no prior constraints on the spectrum except smoothness and non-negativity. In addition, we consider arbitrary modifications to the energy spectrum of the "ordinary" primary source function, fixing its spatial part, finding this alone to be inadequate to explain the PAMELA or WMAP signals. We explore variations in the fits due to choice of magnetic field, primary electron injection index, spatial profiles, propagation parameters, and fit regularization method. Dark matter annihilation fits well, where our fit finds a mass of ~1 TeV and a boost factor times energy fraction of ~70. While it is possible for dark matter decay and pulsars to fit the data, unconventionally high magnetic fields and radiation densities are required near the Galactic Center to counter the relative shallowness of the assumed spatial profiles. We also fit to linear combinations of these three scenarios, though the fit is much less constrained.

astro-ph.CO↗

arXiv2010

A statistical test of emission from unresolved point sources

We describe a simple test of the spatial uniformity of an ensemble of discrete events. Given an estimate for the point source luminosity function and an instrumental point spread function (PSF), a robust upper bound on the fractional point source contribution to a diffuse signal can be found. We verify with Monte Carlo tests that the statistic has advantages over the two-point correlation function for this purpose, and derive analytic estimates of the statistic's mean and variance as a function of the point source contribution. As a case study, we apply this statistic to recent gamma-ray data from the Fermi Large Area Telescope (LAT), and demonstrate that at energies above 10 GeV, the contribution of unresolved point sources to the diffuse emission is small in the region relevant for study of the WMAP Haze.

astro-ph.HE↗

arXiv2010

The Fermi Haze: A Gamma-Ray Counterpart to the Microwave Haze

The Fermi Gamma-Ray Space Telescope reveals a diffuse inverse Compton signal in the inner Galaxy with a similar spatial morphology to the microwave haze observed by WMAP, supporting the synchrotron interpretation of the microwave signal. Using spatial templates, we regress out pi0 gammas, as well as IC and bremsstrahlung components associated with known soft-synchrotron counterparts. We find a significant gamma-ray excess towards the Galactic center with a spectrum that is significantly harder than other sky components and is most consistent with IC from a hard population of electrons. The morphology and spectrum are consistent with it being the IC counterpart to the electrons which generate the microwave haze seen at WMAP frequencies. In addition, the implied electron spectrum is hard; electrons accelerated in supernova shocks in the disk which then diffuse a few kpc to the haze region would have a softer spectrum. We describe the full sky Fermi maps used in this analysis and make them available for download.

astro-ph.HE↗

arXiv2009

The Case for a 700+ GeV WIMP: Cosmic Ray Spectra from PAMELA, Fermi and ATIC

Multiple lines of evidence indicate an anomalous injection of high-energy e+- in the Galactic halo. The recent $e^+$ fraction spectrum from the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) shows a sharp rise up to 100 GeV. The Fermi Gamma-ray Space Telescope has found a significant hardening of the e+e- cosmic ray spectrum above 100 GeV, with a break, confirmed by HESS at around 1 TeV. The Advanced Thin Ionization Calorimeter (ATIC) has also detected detected a similar excess, falling back to the expected spectrum at 1 TeV and above. Excess microwaves towards the galactic center in the WMAP data are consistent with hard synchrotron radiation from a population of 10-100 GeV e+- (the WMAP ``Haze''). We argue that dark matter annihilations can provide a consistent explanation of all of these data, focusing on dominantly leptonic modes, either directly or through a new light boson. Normalizing the signal to the highest energy evidence (Fermi and HESS), we find that similar cross sections provide good fits to PAMELA and the Haze, and that both the required cross section and annihilation modes are achievable in models with Sommerfeld-enhanced annihilation. These models naturally predict significant production of gamma rays in the galactic center via a variety of mechanisms. Most notably, there is a robust inverse-Compton scattered (ICS) gamma-ray signal arising from the energetic electrons and positrons, detectable at Fermi/GLAST energies, which should provide smoking gun evidence for this production.

astro-ph↗

arXiv2009

The Fermi gamma-ray spectrum of the inner galaxy: Implications for annihilating dark matter

Recently, a preliminary spectrum from the Fermi Gamma-ray Space Telescope has been presented for the inner galaxy (-30 < l < 30, -5 < b < 5), as well as the galactic center (-1 < l < 1, -1< b < 1). We consider the implications of these data for dark matter annihilation models, especially models capable of producing the cosmic-ray excesses previously observed by PAMELA and Fermi. These local cosmic-ray excesses, when extrapolated to the inner galaxy, imply inverse Compton scattering (ICS) gamma-ray signals largely consistent with the preliminary Fermi gamma-ray spectrum. For specific halos and models, particularly those with prompt photons, the data have begun to constrain the allowed parameter space. Although significant modeling and background uncertainties remain, we explore how large a signal is permitted by the current data. Based upon this, we make predictions for what signal could be present in other regions of the sky where dark matter signals may be easier to isolate from the astrophysical backgrounds.

astro-ph.HE↗