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We report on a sensitive search for H2 1-0 S(1), 1-0 S(0) and 2-1 S(1)ro-vibrational emission at 2.12, 2.22 and 2.25 micron in a sample of 15 HerbigAe/Be stars employing CRIRES, the ESO-VLT near-infrared high-resolutionspectrograph, at R~90,000. We detect the H2 1-0 S(1) line toward HD 100546 andHD 97048. In the other 13 targets, the line is not detected. The H2 1-0 S(0)and 2-1 S(1) lines are undetected in all sources. This is the first detectionof near-IR H2 emission in HD 100546. The H2 1-0 S(1) lines observed in HD100546 and HD 97048 are observed at a velocity consistent with the restvelocity of both stars, suggesting that they are produced in the circumstellardisk. In HD 97048, the emission is spatially resolved and it is observed toextend at least up to 200 AU. We report an increase of one order of magnitudein the H2 1-0 S(1) line flux with respect to previous measurements taken in2003 for this star, which suggests line variability. In HD 100546 the emissionis tentatively spatially resolved and may extend at least up to 50 AU. Modelingof the H2 1-0 S(1) line profiles and their spatial extent with flat kepleriandisks shows that most of the emission is produced at a radius >5 AU. Upperlimits to the H2 1-0 S(0)/ 1-0 S(1) and H2 2-1 S(1)/1-0 S(1) line ratios in HD97048 are consistent with H2 gas at T>2000 K and suggest that the emissionobserved may be produced by X-ray excitation. The upper limits for the lineratios for HD 100546 are inconclusive. Because the H2 emission is located atlarge radii, for both sources a thermal emission scenario (i.e., gas heated bycollisions with dust) is implausible. We argue that the observation of H2emission at large radii may be indicative of an extended disk atmosphere atradii >5 AU. This may be explained by a hydrostatic disk in which gas and dustare thermally decoupled or by a disk wind caused by photoevaporation.

A survey for near-infrared H2 emission in Herbig Ae/Be stars: emission from the outer disks of HD 97048 and HD 100546